A006689 -id:A006689 - cp's OEIS frontend

A082166 a(n) = A006689(n)/n^2.

1, 3, 24, 328, 6427, 164765, 5228210, 197897582, 8704544263, 436312502297, 24550259053858, 1532241939881294, 105048412352334420, 7847739530288388636, 634523723233529394594, 55206024491463561241758, 5142697402316326354705599, 510704188733699181740089521, 53858874208665420063477867788

Offset: 1

Valery A. Liskovets, Apr 09 2003

Valery A. Liskovets, The number of initially connected automata, Kibernetika, (Kiev), No3 (1969), 16-19; Engl. transl.: Cybernetics, v.4 (1969), 259-262.

Valery A. Liskovets, Exact enumeration of acyclic automata, Proc. 15th Conf. "Formal Power Series and Algebr. Combin. (FPSAC'03)", 2003.
Valery A. Liskovets, Exact enumeration of acyclic deterministic automata, Discrete Appl. Math., 154, No.3 (2006), 537-551.

Cf. A006689.

b[n_] := b[n] = If[n == 1, 1, n^(2*n)/(n-1)! - Sum[n^(2*(n-i))*b[i]/(n-i)!, {i, 1, n-1}]];
a[n_] := b[n]/n^2;
Array[a, 16] (* Jean-François Alcover, Aug 28 2019 *)

A082165 Duplicate of A006689.

Original entry on oeis.org

1, 12, 216, 5248, 160675, 5931540, 256182290, 12665445248, 705068085303

Offset: 1

dead

A006690 Number of deterministic, completely-defined, initially-connected finite automata with 3 inputs and n unlabeled states.

Original entry on oeis.org

1, 56, 7965, 2128064, 914929500, 576689214816, 500750172337212, 572879126392178688, 835007874759393878655, 1510492370204314777345000, 3320470273536658970739763334, 8718034433102107344888781813632, 26945647825926481227016730431025962, 96843697086370972449408988324175689680

Offset: 1

N. J. A. Sloane

a(n) is divisible by n^3, see A082168. These automata have no nontrivial automorphisms (by states).
Found in column 0 of triangle A107676, which is the matrix cube of triangle A107671 (see recurrence formulas). - Paul D. Hanna, Jun 07 2005
A complete initially connected deterministic finite automaton (icdfa) with n states in an alphabet of k symbols can be represented by a special string of {0,...,n-1}^* with length kn. In that string, let f_i be the index of the first occurrence of state i (used in the formula). - Nelma Moreira, Jul 31 2005
This is H_3(n) in Liskovets (DAM, Vol. 154, 2006), p. 548; the formula for H_k is given in Eq. (11), p. 546. - M. F. Hasler, May 16 2018

R. Bacher and C. Reutenauer, The number of right ideals of given codimension over a finite field, in Noncommutative Birational Geometry, Representations and Combinatorics, edited by Arkady. Berenstein and Vladimir. Retakha, Contemporary Mathematics, Vol. 592, 2013.
V. A. Liskovets, The number of initially connected automata, Kibernetika, (Kiev), No3 (1969), 16-19; Engl. transl.: Cybernetics, v.4 (1969), 259-262.
R. Reis, N. Moreira and M. Almeida, On the Representation of Finite Automata, in Proocedings of 7th Int. Workshop on Descriptional Complexity of Formal Systems (DCFS05) Jun 30, 2005, Como, Italy, page 269-276
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

M. Almeida, N. Moreira and R. Reis, On the Representation of Finite Automata, Technical Report DCC-2005-04, DCC - FC & LIACC, Universidade do Porto, April, 2005.
M. Almeida, N. Moreira, R. Reis, Enumeration and generation with a string automata representation, Theor. Comp. Sci. 387 (2007), 93-102; see B(k=3,n).
Valery A. Liskovets, The number of connected initial automata, Kibernetika (Kiev), 3 (1969), 16-19 (in Russian; English translation: Cybernetics, 4 (1969), 259-262).
Valery A. Liskovets, Exact enumeration of acyclic automata, Proc. 15th Conf. "Formal Power Series and Algebr. Combin. (FPSAC'03)", 2003.
Valery A. Liskovets, Exact enumeration of acyclic deterministic automata, Discrete Appl. Math., 154, No. 3 (2006), 537-551.
Robert W. Robinson, Counting strongly connected finite automata, pages 671-685 in "Graph theory with applications to algorithms and computer science." Proceedings of the fifth international conference held at Western Michigan University, Kalamazoo, Mich., June 4-8, 1984. Edited by Y. Alavi, G. Chartrand, L. Lesniak [L. M. Lesniak-Foster], D. R. Lick and C. E. Wall. A Wiley-Interscience Publication. John Wiley & Sons, Inc., New York, 1985. xv+810 pp. ISBN: 0-471-81635-3; Math Review MR0812651. (86g:05026). [Annotated scanned copy, with permission of the author.]

Cf. A006689, A006689, A107671, A107676.

b := proc(k,n)
    option remember;
    if n = 1 then
        1;
    else
        n^(k*n) -add(binomial(n-1,j-1)*n^(k*(n-j))*procname(k,j),j=1..n-1) ;
    end if;
end proc:
B := proc(k,n)
    b(k,n)/(n-1)! ;
end proc:
A006690 := proc(n)
    B(3,n) ;
end proc:
seq(A006690(n),n=1..10) ; # R. J. Mathar, May 21 2018

a[1] = 1; a[n_] := a[n] = n^(3*n)/(n-1)! - Sum[n^(3*(n-i))*a[i]/(n-i)!, {i, 1, n-1}]; Table[a[n], {n, 1, 11}] (* Jean-François Alcover, Dec 15 2014 *)

{a(n)=local(P=matrix(n+1,n+1,r,c,if(r>=c,(r^3)^(r-c)/(r-c)!)), D=matrix(n+1,n+1,r,c,if(r==c,r)));(P^-1*D^3*P)[n+1,1]} \\ Paul D. Hanna, Jun 07 2005

A6690=[1];A006690(n)={for(n=#A6690+1,n,A6690=concat(A6690,n^(3*n)/(n-1)!-sum(k=1,n-1,n^(3*k)*A6690[n-k]/k!)));A6690[n]} \\ M. F. Hasler, May 16 2018

a(n) = h_3(n)/(n-1)!, where h_3(1) := 1, h_3(n) := n^(3*n) - Sum_{i=1..n-1} binomial(n-1, i-1) * n^(3*n-3*i) * h_3(i) for n > 1.

For k = 3, a(n) = Sum (Product_{i=1..n-1} i^(f_i - f_{i-1} - 1))) * n^(n*k - f_{n-1} - 1), where the sum is taken over integers f_1, ..., f_{n-1} satisfying 0 <= f_1 < k and f_{i-1} < f_{i} < i*k for i = 2..n-1. - Nelma Moreira, Jul 31 2005 [Typo corrected by Petros Hadjicostas, Mar 06 2021. See Theorem 8 in Almeida, Moreira, and Reis (2007). The value of f_0 is not relevant.]

a(11) and more detailed definition from Valery A. Liskovets, Apr 09 2003
Edited by N. J. A. Sloane, Dec 06 2008 at the suggestion of R. J. Mathar
More terms from M. F. Hasler, May 16 2018

A006691 Normalized number of connected (n+1)-state finite automata with 2 inputs.

Original entry on oeis.org

9, 148, 3493, 106431, 3950832, 172325014, 8617033285, 485267003023, 30363691715629, 2088698040637242, 156612539215405732, 12709745319947141220, 1109746209390479579732, 103724343230007402591558, 10332348604630683943445797, 1092720669631704348689818959, 122274820828415241343176467043

Offset: 1

N. J. A. Sloane

nonn

Is this sequence essentially the same as A304312? - Paul D. Hanna, May 11 2018
From Petros Hadjicostas, Feb 26 2021: (Start)
See Table 2 (p. 683) in Robinson (1984) for values of S(p)/(p-1)! = S(p,d)/(p-1)! with p >= 2 and d = 2. In the paper, S(p) = S(p,d) is the number of (labeled) strongly connected finite automata with state set {1, 2, ..., p} and d inputs (p. 680). Since the offset here is 1, the original name of the sequence was changed to read "(n+1)-state" from "n-state".
This change agrees with Valery A. Liskovets's formula below, who was the first one to derive expressions for the quantity S(p) = S(p,d) for a general d more than a decade before Robinson (1984). See Liskovets (1971), where S(p) = S(p,d), with d inputs, is denoted by sigma_r(n) with r = d (inputs) and n = p (number of states). For d = 2, the values of S(p) = S(p,d=2) = (p-1)!*a(p-1) for p >= 1 (with a(0) := 1) are given in A027834, which has the correct name.
We may suggest two possible names for a(n): (i) the normalized number of labeled strongly connected (n+1)-state finite automata with 2 inputs, or (ii) the number of unlabeled strongly connected (n+1)-state finite automata with 2 inputs and a starting gate. (For purely unlabeled strongly connected n-state finite automata with 2 inputs, see A027835, whose terms are calculated based on Valery A. Liskovets' formulas.) (End)

Robert W. Robinson, Counting strongly connected finite automata, pages 671-685 in "Graph theory with applications to algorithms and computer science." Proceedings of the fifth international conference held at Western Michigan University, Kalamazoo, Mich., June 4-8, 1984. Edited by Y. Alavi, G. Chartrand, L. Lesniak [L. M. Lesniak-Foster], D. R. Lick and C. E. Wall. A Wiley-Interscience Publication. John Wiley & Sons, Inc., New York, 1985. xv+810 pp. ISBN: 0-471-81635-3; Math Review MR0812651 (86g:05026).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Hugo Pfoertner, Table of n, a(n) for n = 1..200
Valery A. Liskovets [ Liskovec ], Enumeration of nonisomorphic strongly connected automata, (in Russian); Vesti Akad. Nauk. Belarus. SSR, Ser. Phys.-Mat., No. 3, 1971, pp. 26-30, esp. p. 30 (Math. Rev. 46 #5081; Zentralblatt 224 #94053).
Valery A. Liskovets [ Liskovec ], A general enumeration scheme for labeled graphs, (in Russian); Dokl. Akad. Nauk. Belarus. SSR, Vol. 21, No. 6 (1977), pp. 496-499 (Math. Rev. 58 #21797; Zentralblatt 412 #05052).
R. W. Robinson, Counting strongly connected finite automata, pages 671-685 in "Graph theory with applications to algorithms and computer science." Proceedings of the fifth international conference held at Western Michigan University, Kalamazoo, Mich., June 4-8, 1984. Edited by Y. Alavi, G. Chartrand, L. Lesniak [L. M. Lesniak-Foster], D. R. Lick and C. E. Wall. A Wiley-Interscience Publication. John Wiley & Sons, Inc., New York, 1985. xv+810 pp. ISBN: 0-471-81635-3; Math Review MR0812651. (86g:05026). [Annotated scanned copy, with permission of the author.]

Cf. A027834, A304312.

v[r_, n_] := v[r, n] = If[n == 0, 1, n^(r*n) - Sum[Binomial[n, t] * n^(r*(n - t)) * v[r, t] , {t, 1, n - 1}]];
s[r_, n_] := s[r, n] = v[r, n] + Sum[Binomial[n - 1, t - 1] * v[r, n - t] * s[r, t], {t, 1, n - 1}]
A027834[n_] := s[2, n];
a[n_] := A027834[n + 1]/n!;
Array[a, 28] (* Jean-François Alcover, Aug 27 2019 *)

a(n) = A027834(n+1)/n!. - Valery A. Liskovets, May 21 2018

Extended using the formula by Valery A. Liskovets by Hugo Pfoertner, May 21 2018

Name edited by Petros Hadjicostas, Feb 26 2021 to agree with Robinson's and Liskovets' papers.

A107667 Triangular matrix T, read by rows, that satisfies: T = D + SHIFT_LEFT(T^2) where SHIFT_LEFT shifts each row 1 place to the left and D is the diagonal matrix {1, 2, 3, ...}.

Original entry on oeis.org

1, 4, 2, 45, 9, 3, 816, 112, 16, 4, 20225, 2200, 225, 25, 5, 632700, 58176, 4860, 396, 36, 6, 23836540, 1920163, 138817, 9408, 637, 49, 7, 1048592640, 75683648, 4886464, 290816, 16576, 960, 64, 8, 52696514169, 3460349970, 203451912, 10948203, 553473

Offset: 0

Paul D. Hanna, Jun 07 2005

			Reverse of rows form the initial terms of g.f.s below.
Row n=0: 1 = 1*(1-x) + 1*x*(1-x) + ...
Row n=1: 2 = 2*(1-2*x) + 4*x*(1-2*x)*(1-x) + 12*x^2*(1-2*x)*(1-x) + ...
Row n=2: 3 = 3*(1-3*x) + 9*x*(1-3*x)*(1-2*x)
           + 45*x^2*(1-3*x)*(1-2*x)*(1-x)
           + 216*x^3*(1-3*x)*(1-2*x)*(1-x) + ...
Row n=3: 4 = 4*(1-4*x) + 16*x*(1-4*x)*(1-3*x)
           + 112*x^2*(1-4*x)*(1-3*x)*(1-2*x)
           + 816*x^3*(1-4*x)*(1-3*x)*(1-2*x)*(1-x)
           + 5248*x^4*(1-4*x)*(1-3*x)*(1-2*x)*(1-x) + ...
Triangle T begins:
           1;
           4,        2;
          45,        9,       3;
         816,      112,      16,      4;
       20225,     2200,     225,     25,     5;
      632700,    58176,    4860,    396,    36,   6;
    23836540,  1920163,  138817,   9408,   637,  49,  7;
  1048592640, 75683648, 4886464, 290816, 16576, 960, 64, 8;
  ...
The matrix square T^2 shifts each row right 1 place, dropping the diagonal D and putting A006689 in column 0:
          1;
         12,        4;
        216,       45,       9;
       5248,      816,     112,     16;
     160675,    20225,    2200,    225,   25;
    5931540,   632700,   58176,   4860,  396,  36;
  256182290, 23836540, 1920163, 138817, 9408, 637, 49;
  ...

Cf. A006689, A107668 (column 0), A107669, A107670 (matrix square).

a = [[sum [a!!n!!i * a!!i!!(k+1) | i<-[k+1..n]] | k <- [0..n-1]] ++ [fromIntegral n+1] | n <- [0..]]

{T(n,k)=local(P=matrix(n+1,n+1,r,c,if(r>=c,(r^2)^(r-c)/(r-c)!)), D=matrix(n+1,n+1,r,c,if(r==c,r)));if(n>=k,(P^-1*D*P)[n+1,k+1])}

Matrix diagonalization method: define the triangular matrix P by P(n, k) = ((n+1)^2)^(n-k)/(n-k)! for n >=k >= 0 and the diagonal matrix D by D(n, n) = n+1 for n >= 0; then T is given by T = P^-1*D*P.

Rows read in reverse form the initial terms of the g.f.: (n+1) = Sum_{k>=0} T(n, n-k) * x^k * Product_{j=0..k} (1-(n+1-j)*x) = T(n, n)*(1-(n+1)*x) + T(n, n-1)*x*(1-(n+1)*x)*(1-n*x) + T(n, n-2)*x^2*(1-(n+1)*x)*(1-n*x)*(1-(n-1)*x) + ... [Corrected by Petros Hadjicostas, Mar 11 2021]

A027834 Number of labeled strongly connected n-state 2-input automata.

Original entry on oeis.org

1, 9, 296, 20958, 2554344, 474099840, 124074010080, 43429847756400, 19565965561887360, 11018376449767451520, 7579467449864423769600, 6251471405353507523097600, 6087988343847192559805952000, 6910412728595671664966422425600, 9042510998634333921282477985689600

Offset: 1

N. J. A. Sloane

nonn

Hugo Pfoertner, Table of n, a(n) for n = 1..200
Michael A. Harrison, A census of finite automata, Canadian Journal of Mathematics, 17 (1965), 100-113.
Valery A. Liskovets [ Liskovec ], Enumeration of nonisomorphic strongly connected automata, (in Russian); Vesti Akad. Nauk. Belarus. SSR, Ser. Phys.-Mat., No. 3, 1971, pp. 26-30, esp. p. 30 (Math. Rev. 46 #5081; Zentralblatt 224 #94053).
Valery A. Liskovets [ Liskovec ], A general enumeration scheme for labeled graphs, (in Russian); Dokl. Akad. Nauk. Belarus. SSR, Vol. 21, No. 6 (1977), pp. 496-499 (Math. Rev. 58 #21797; Zentralblatt 412 #05052).
Robert W. Robinson, Counting strongly connected finite automata, in: Graph Theory with Applications to Graph Theory and Computer Science, Wiley, 1985, pp. 671-685.

Cf. A006689, A006691, A027835.

v[r_, n_] := If[n == 0, 1, n^(r*n) - Sum[Binomial[n, t] * n^(r*(n - t)) * v[r, t], {t, 1, n - 1}]];
s[r_, n_] := v[r, n] + Sum[Binomial[n - 1, t - 1] * v[r, n - t] * s[r, t], {t, 1, n - 1}];
a[n_] := s[2, n];
Array[a, 15] (* Jean-François Alcover, Aug 27 2019, from PARI *)

/* a(n) = s_2(n) using a formula (Th.2) of Valery Liskovets: */
{v(r,n) = if(n==0,1, n^(r*n) - sum(t=1,n-1, binomial(n,t) * n^(r*(n-t)) * v(r,t) ))}
{s(r,n) = v(r,n) + sum(t=1,n-1, binomial(n-1,t-1) * v(r,n-t) * s(r,t) )}
for(n=1,20,print1( s(r=2, n),", ")) \\ Paul D. Hanna, May 16 2018

a(n) = A006691(n-1)*(n-1)! for n >= 1 (with A006691(0) := 1). [This is a restatement of Valery A. Liskovets' formula in A006691. The original name of A006691 was edited accordingly. - Petros Hadjicostas, Feb 26 2021]

Sequence extended (a(7)-a(15)) by Paul D. Hanna using a formula by Valery A. Liskovets.

A342202 T(n,k) = V(n,k)/k!, where V(n,k) = k^(nk) - Sum_{t=1..k-1} binomial(k,t)k^(n(k-t))V(n,t) for n, k >= 1; square array T read by upwards antidiagonals.

Original entry on oeis.org

1, 1, 0, 1, 4, 0, 1, 24, 45, 0, 1, 112, 2268, 816, 0, 1, 480, 76221, 461056, 20225, 0, 1, 1984, 2245320, 152978176, 160977375, 632700, 0, 1, 8064, 62858025, 43083161600, 673315202500, 85624508376, 23836540, 0, 1, 32512, 1723364748, 11442561314816, 2331513459843750, 5508710472669120, 64363893844726, 1048592640, 0

Offset: 1

Petros Hadjicostas, Mar 04 2021

To prove Paul D. Hanna's formula for the row n o.g.f. A(x,n) = Sum_{m >= 1} T(n,m)*x^m, we use Leibniz's rule for the k-th derivative of a product of functions: dx^k(exp(k^n*x) * (1 - A(x,n)))/dx = Sum_{s=0..k} binomial(k,s) * d^s(exp(k^n*x))/dx^s * d^(k-s) (1 - A(x,n))/dx^(k-s) = k^(n*k) * exp(k^n*x) * (1 - Sum_{m>=1} T(n,m) * x^m) - Sum_{s=0..k-1} binomial(k,s) * k^(n*s) * exp(k^n*x) * (Sum_{m>=1} (m!/(m-(k-s))!) * T(n,m) * x^(m-(k-s))). The coefficient of x^k for exp(k^n*x) * (1 - A(x,n)) is obtained by setting x = 0 in the k-the derivative, and it is equal to k^(n*k) - Sum_{s=0..k-1} binomial(k,s) * k^(n*s) * (k-s)! * T(n,k-s) = k! * (k^(n*k)/k! - Sum_{s=0..k-1} k^(n*s)/s! * T(n,k-s)) = 0 because of the recurrence that T(n,k) satisfies.
To prove the formula below for T(n,k) that involves the compositions of k, we use mathematical induction on k. For k = 1, it is obvious. Assume it is true for all n and all m < k. Consider the compositions of k.
There is only one of size r = 1, namely k, and corresponds to the term k^(n*k)/k! in the recurrence T(n,k) = k^(n*k)/k! - Sum_{s=1..k-1} k^(n*s)/s! * T(n,k-s).
For the other compositions (s_1, ..., s_r) of k (of any size r >= 2), we group them according to the their last element s_r = s in {1, 2, ..., k - 1}, which gives rise to the factor k^(n*s)/s! = (Sum_{i=1..r} s_i)^(n*s_r)/s_r!. Using the inductive hypothesis, we substitute the expression for T(n,k-s) in the recurrence T(n,k) = k^(n*k)/k! - Sum_{s=1..k-1} k^(n*s)/s! * T(n,k-s). Each term in the expression for T(n,k-s) corresponds to a composition of k - s and is postmultiplied by k^(n*s)/s! = (Sum_{i=1..r} s_i)^(n*s_r)/s_r!. We thus get a term in the expression for T(n,k) that corresponds to a composition of the form (composition of k - s) + s, and the sign of this term is (-1)^((size of composition of k - s) + 1). The rest of the proof follows easily.

			Square array T(n,k) (n, k >= 1) begins:
  1,    0,        0,              0,                   0, ...
  1,    4,       45,            816,               20225, ...
  1,   24,     2268,         461056,           160977375, ...
  1,  112,    76221,      152978176,        673315202500, ...
  1,  480,  2245320,    43083161600,    2331513459843750, ...
  1, 1984, 62858025, 11442561314816, 7570813415735296875, ...
  ...

Michael A. Harrison, A census of finite automata, Canadian Journal of Mathematics, 17 (1965), 100-113.
Valery A. Liskovets [ Liskovec ], Enumeration of nonisomorphic strongly connected automata, (in Russian); Vesti Akad. Nauk. Belarus. SSR, Ser. Phys.-Mat., No. 3, 1971, pp. 26-30, esp. p. 30 (Math. Rev. 46 #5081; Zentralblatt 224 #94053).
Valery A. Liskovets [ Liskovec ], A general enumeration scheme for labeled graphs, (in Russian); Dokl. Akad. Nauk. Belarus. SSR, Vol. 21, No. 6 (1977), pp. 496-499 (Math. Rev. 58 #21797; Zentralblatt 412 #05052).
Michel Marcus, PARI program that implements the formula for T(n,k) that involves compositions of k, 2021.
Robert W. Robinson, Counting strongly connected finite automata, in: Graph Theory with Applications to Graph Theory and Computer Science, Wiley, 1985, pp. 671-685.

Cf. A027834, A027835, A059153 (shifted column 2), A342405 (column 3).

Shifted rows: A000007 (row 1), A107668 (row 2), A107675 (row 3), A304394 (row 4), A304395 (row 5).

/* The recurrence for V(n,k) is due to Valery A. Liskovets. See his 1971 paper. A second program that implements the formula above involving the compositions of k appears in the links and was written by Michel Marcus. */
V(n,k) = k^(n*k) - sum(t=1, k-1, binomial(k, t)*k^(n*(k-t))*V(n,t));
T(n,k) = V(n,k)/k!

T(n,k) = k^(n*k)/k! - Sum_{s=1..k-1} k^(n*s)/s! * T(n,k-s).
For each n >= 1, the row n o.g.f. A(x,n) = Sum_{k >= 1} T(n,k)*x^k satisfies [x^k] (exp(k^n*x) * (1 - A(x,n))) = 0 for each k >= 1. (This is Paul D. Hanna's formula from the shifted rows 2-5: A107668, A107675, A304394, A304395.)
A027834(k) = T(2, k)*k! + Sum_{t=1..k-1} binomial(k-1, t-1) * T(2, k-t) * (k-t)! * A027834(t), where A027834(k) = number of strongly connected k-state 2-input automata. (See Theorem 2 in Valery A. Liskovets's 1971 paper.)
T(n,k) = Sum_{r=1..k} (-1)^(r-1) * Sum_{s_1, ..., s_r} (1/(Product_{j=1..r} s_j!)) * Product_{j=1..r} (Sum_{i=1..j} s_i)^(n*s_j)), where the second sum is over lists (s_1, ..., s_r) of positive integers s_i such that Sum_{i=1..r} s_i = k. (Thus the second sum is over all ordered partitions (i.e., compositions) of k.)
T(n,k=1) = 1 and T(n,k=2) = 2^n*(2^(n-1) - 1) = A059153(n-2) (with A059153(-1) := 0).
T(n,k=3) = (27^n - 3*9^n - 3*12^n)/6 + 6^n.
T(n,k=4) = 256^n/24 - (5/12)*64^n - 108^n/6 + 32^n/2 + 36^n/2 + 48^n/2 - 24^n.

A006692 Number of connected n-state finite automata with 3 inputs.

Original entry on oeis.org

49, 6877, 1854545, 807478656, 514798204147, 451182323794896, 519961864703259753, 762210147961330421167, 1384945048774500147047194, 3055115321627096660341307614, 8043516699726480852467167758419, 24915939138210507189761922944830006, 89709850983809128394441772076036629240

Offset: 1

N. J. A. Sloane

nonn

Is this sequence essentially the same as A304313? - Paul D. Hanna, May 11 2018

Robert W. Robinson, Counting strongly connected finite automata, pages 671-685 in "Graph theory with applications to algorithms and computer science." Proceedings of the fifth international conference held at Western Michigan University, Kalamazoo, Mich., June 4-8, 1984. Edited by Y. Alavi, G. Chartrand, L. Lesniak [L. M. Lesniak-Foster], D. R. Lick and C. E. Wall. A Wiley-Interscience Publication. John Wiley & Sons, Inc., New York, 1985. xv+810 pp. ISBN: 0-471-81635-3; Math Review MR0812651 (86g:05026).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Hugo Pfoertner, Table of n, a(n) for n = 1..200
R. W. Robinson, Counting strongly connected finite automata, pages 671-685 in "Graph theory with applications to algorithms and computer science." Proceedings of the fifth international conference held at Western Michigan University, Kalamazoo, Mich., June 4-8, 1984. Edited by Y. Alavi, G. Chartrand, L. Lesniak [L. M. Lesniak-Foster], D. R. Lick and C. E. Wall. A Wiley-Interscience Publication. John Wiley & Sons, Inc., New York, 1985. xv+810 pp. ISBN: 0-471-81635-3; Math Review MR0812651. (86g:05026). [Annotated scanned copy, with permission of the author.]

Cf. A027834, A006691, A304313.

Extended using the PARI program by Paul D. Hanna in A027834 by Hugo Pfoertner, May 22 2018

A027835 Number of unlabeled strongly connected n-state 2-input automata.

Original entry on oeis.org

1, 6, 52, 892, 21291, 658885, 24617866, 1077142765, 53918557215, 3036369842197, 189881640057942, 13051044976503663, 977672716919010876, 79267586388173032966, 6914956215333832011058, 645771787789692953182732, 64277686448923785217048191, 6793045601578652098886514581, 759656437858515775195264228768, 89619947709601175930862298926038

Offset: 1

N. J. A. Sloane

nonn

Michael A. Harrison, A census of finite automata, Canadian Journal of Mathematics, 17 (1965), 100-113.
Valery A. Liskovets [ Liskovec ], Enumeration of nonisomorphic strongly connected automata, (in Russian); Vesti Akad. Nauk. Belarus. SSR, Ser. Phys.-Mat., No. 3, 1971, pp. 26-30, esp. p. 30 (Math. Rev. 46 #5081; Zentralblatt 224 #94053).
Valery A. Liskovets [ Liskovec ], A general enumeration scheme for labeled graphs, (in Russian); Dokl. Akad. Nauk. Belarus. SSR, Vol. 21, No. 6 (1977), pp. 496-499 (Math. Rev. 58 #21797; Zentralblatt 412 #05052).

Cf. A006689, A027834.

{v(r, n) = if(n==0, 1, n^(r*n) - sum(t=1, n-1, binomial(n, t) * n^(r*(n-t)) * v(r, t) ))}
{s(r, n) = v(r, n) + sum(t=1, n-1, binomial(n-1, t-1) * v(r, n-t) * s(r, t) )} \\ This is Paul D. Hanna's PARI program from A027834 regarding s(r,n) = number of labeled strongly connected n-state r-input automata.
{SS(r,n) = (1/n)*sumdiv(n, m, (s(r,m)/(m-1)!)*sumdiv(n/m, d, moebius(n/(m*d))*d^((r-1)*m+1)))} \\ This calculates the number of unlabeled strongly connected n-state r-input automata. It is Valery A. Liskovets's formula from his 1971 paper.
for(n=1, 20, print1( SS(r=2, n), ", ")) \\ Petros Hadjicostas, Feb 26 2021

More terms from Petros Hadjicostas, Feb 26 2021 using formula (5), p. 28, in Liskovets (1971)

A107670 Matrix square of triangle A107667.

Original entry on oeis.org

1, 12, 4, 216, 45, 9, 5248, 816, 112, 16, 160675, 20225, 2200, 225, 25, 5931540, 632700, 58176, 4860, 396, 36, 256182290, 23836540, 1920163, 138817, 9408, 637, 49, 12665445248, 1048592640, 75683648, 4886464, 290816, 16576, 960, 64

Offset: 0

Paul D. Hanna, Jun 07 2005

Column 0 is A006689. See triangle A107667 for more formulas.

			Triangle T(n,k) (with rows n >= 0 and columns k = 0..n) begins:
          1;
         12,        4;
        216,       45,       9;
       5248,      816,     112,     16;
     160675,    20225,    2200,    225,   25;
    5931540,   632700,   58176,   4860,  396,  36;
  256182290, 23836540, 1920163, 138817, 9408, 637, 49;
  ...

Cf. A107667, A107668, A107669, A006689 (column 0).

{T(n,k)=local(P=matrix(n+1,n+1,r,c,if(r>=c,(r^2)^(r-c)/(r-c)!)), D=matrix(n+1,n+1,r,c,if(r==c,r)));if(n>=k,(P^-1*D^2*P)[n+1,k+1])}

Matrix diagonalization method: define the triangular matrix P by P(n, k) = ((n+1)^2)^(n-k)/(n-k)! for n >= k >= 0 and the diagonal matrix D by D(n, n) = n+1 for n >= 0; then T is given by T = P^-1*D^2*P.

cp's OEIS Frontend

A082166 a(n) = A006689(n)/n^2.

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A082165 Duplicate of A006689.

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A006690 Number of deterministic, completely-defined, initially-connected finite automata with 3 inputs and n unlabeled states.

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A006691 Normalized number of connected (n+1)-state finite automata with 2 inputs.

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A107667 Triangular matrix T, read by rows, that satisfies: T = D + SHIFT_LEFT(T^2) where SHIFT_LEFT shifts each row 1 place to the left and D is the diagonal matrix {1, 2, 3, ...}.

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A027834 Number of labeled strongly connected n-state 2-input automata.

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A342202 T(n,k) = V(n,k)/k!, where V(n,k) = k^(n*k) - Sum_{t=1..k-1} binomial(k,t)*k^(n*(k-t))*V(n,t) for n, k >= 1; square array T read by upwards antidiagonals.

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A006692 Number of connected n-state finite automata with 3 inputs.

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A342202 T(n,k) = V(n,k)/k!, where V(n,k) = k^(nk) - Sum_{t=1..k-1} binomial(k,t)k^(n(k-t))V(n,t) for n, k >= 1; square array T read by upwards antidiagonals.