cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

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A193678 Discriminant of Chebyshev C-polynomials.

Original entry on oeis.org

1, 8, 108, 2048, 50000, 1492992, 52706752, 2147483648, 99179645184, 5120000000000, 292159150705664, 18260173718028288, 1240576436601868288, 91029559914971267072, 7174453500000000000000, 604462909807314587353088, 54214017802982966177103872
Offset: 1

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Author

Wolfdieter Lang, Aug 07 2011

Keywords

Comments

The array of coefficients of the (monic) Chebyshev C-polynomials is found under A127672 (where they are called, in analogy to the S-polynomials, R-polynomials).
See A127670 for the formula in terms of the square of a Vandermonde determinant, where now the zeros are xn[j]:=2*cos(Pi*(2*j+1)/(2*n)), j=0,..,n-1.
One could add a(0)=0 for the discriminant of C(0,x)=2.
Except for sign, a(n) is the field discriminant of 2^(1/n); see the Mathematica program. - Clark Kimberling, Aug 03 2015

Examples

			n=3: The zeros are [sqrt(3),0,-sqrt(3)]. The Vn(xn[0],..,xn[n-1]) matrix is [[1,1,1],[sqrt(3),0,-sqrt(3)],[3,0,3]]. The squared determinant is 108 = a(3).
		

References

  • Theodore J. Rivlin, Chebyshev polynomials: from approximation theory to algebra and number theory, 2. ed., Wiley, New York, 1990; p. 219 for T and U polynomials.

Crossrefs

Cf. A127670.

Programs

  • Magma
    [(2^(n-1))*n^n: n in [1..20]]; // Vincenzo Librandi, Aug 04 2015
  • Maple
    seq(discrim(2*orthopoly[T](n,x/2), x), n = 1..50); # Robert Israel, Aug 04 2015
  • Mathematica
    t=Table[NumberFieldDiscriminant[2^(1/m)], {m, 1, 20}] (* signed version *)
    Abs[t] (* Clark Kimberling, Aug 03 2015 *)
    Table[(2^(n - 1)) n^n, {n, 20}] (* Vincenzo Librandi, Aug 04 2015 *)

Formula

a(n) = (Det(Vn(xn[0],..,xn[n-1])))^2, with the n x n Vandermonde matrix Vn and the zeros xn[j],j=0..n-1, given above in a comment.
a(n) = (2^(n-1))*n^n, n>=1.
a(n) = A000079(n-1)*A000312(n). - Omar E. Pol, Aug 27 2011

A241299 Initial digit of the decimal expansion of n^(n^n) or n^^3 (in Don Knuth's up-arrow notation).

Original entry on oeis.org

0, 1, 1, 7, 1, 1, 2, 3, 6, 4, 1, 3, 4, 6, 1, 3, 1, 3, 1, 1, 3, 2, 3, 5, 5, 2, 2, 2, 8, 1, 1, 9, 1, 2, 3, 4, 8, 2, 4, 1, 1, 2, 8, 3, 2, 1, 4, 2, 5, 1, 6, 7, 2, 2, 2, 2, 2, 2, 8, 4, 1, 4, 8, 1, 5, 8, 4, 1, 4, 1, 2, 1, 9, 6, 6, 2, 1, 1, 7, 6, 1, 7, 7, 2, 4, 1, 8, 6, 1, 7, 1, 1, 3, 1, 2, 6, 3, 5, 1, 1, 1, 2, 2, 5, 4
Offset: 0

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Author

Keywords

Comments

0^^3 = 0 since 0^^k = 1 for even k, 0 for odd k, k >= 0.
Conjecture: the distribution of the initial digits obey Zipf's law.
The distribution of the first 1000 terms beginning with 1: 302, 196, 124, 91, 72, 46, 71, 53, 45.

Examples

			a(0) = 0, a(1) = 1, a(2) = 1 because 2^(2^2) = 16, a(3) = 7 because 3^(3^3) = 7625597484987 and its initial digit is 7, etc.
		

Crossrefs

Programs

  • Mathematica
    g[n_] := Quotient[n^p, 10^(Floor[ p*Log10@ n] - (1004 + p))]; f[n_] := Block[{p = n}, Quotient[ Nest[ g@ # &, p, p], 10^(1004 + p)]]; Array[f, 105, 0]

Formula

For n > 0, a(n) = floor(t/10^floor(log_10(t))) where t = n^(n^n).
a(n) = A000030(A002488(n)). - Omar E. Pol, Jul 04 2019

A245667 Number T(n,k) of sequences in {1,...,n}^n with longest increasing subsequence of length k; triangle T(n,k), n>=0, 0<=k<=n, read by rows.

Original entry on oeis.org

1, 0, 1, 0, 3, 1, 0, 10, 16, 1, 0, 35, 175, 45, 1, 0, 126, 1771, 1131, 96, 1, 0, 462, 17906, 23611, 4501, 175, 1, 0, 1716, 184920, 461154, 161876, 13588, 288, 1, 0, 6435, 1958979, 8837823, 5179791, 759501, 34245, 441, 1, 0, 24310, 21253375, 169844455, 157279903, 36156355, 2785525, 75925, 640, 1
Offset: 0

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Author

Alois P. Heinz, Jul 28 2014

Keywords

Comments

Sum_{k=0..1} T(n,k) = A088218(n).
Sum_{k=0..2} T(n,k) = A239295(n).
Sum_{k=0..3} T(n,k) = A239299(n).
Sum_{k=1..n} k * T(n,k) = A275576(n).

Examples

			T(3,1) = 10: [1,1,1], [2,1,1], [2,2,1], [2,2,2], [3,1,1], [3,2,1], [3,2,2], [3,3,1], [3,3,2], [3,3,3].
T(3,3) = 1: [1,2,3].
Triangle T(n,k) begins:
  1;
  0,    1;
  0,    3,      1;
  0,   10,     16,      1;
  0,   35,    175,     45,      1;
  0,  126,   1771,   1131,     96,     1;
  0,  462,  17906,  23611,   4501,   175,   1;
  0, 1716, 184920, 461154, 161876, 13588, 288,  1;
  ...
		

Crossrefs

Columns k=0-10 give: A000007, A088218 or A001700(n-1) for n>0, A268869, A268870, A268871, A268872, A268873, A268874, A268875, A268876, A268877.
Main diagonal gives A000012.
T(n,n-1) gives A152618(n) for n>0.
T(n,n-2) gives A268936(n).
T(2n,n) gives A268949(n).
Row sums give A000312.

Programs

  • Maple
    b:= proc(n, l) option remember; `if`(n=0, 1, add(b(n-1, [seq(min(l[j],
          `if`(j=1 or l[j-1] `if`(k=0, `if`(n=0, 1, 0), b(n, [n$k])):
    T:= (n, k)-> A(n, k) -`if`(k=0, 0, A(n, k-1)):
    seq(seq(T(n, k), k=0..n), n=0..9);
  • Mathematica
    b[n_, l_List] := b[n, l] = If[n == 0, 1, Sum[b[n-1, Table[Min[l[[j]], If[j == 1 || l[[j-1]]Jean-François Alcover, Feb 04 2015, after Alois P. Heinz *)

A008785 a(n) = (n+4)^n.

Original entry on oeis.org

1, 5, 36, 343, 4096, 59049, 1000000, 19487171, 429981696, 10604499373, 289254654976, 8649755859375, 281474976710656, 9904578032905937, 374813367582081024, 15181127029874798299, 655360000000000000000, 30041942495081691894741, 1457498964228107529355264
Offset: 0

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Author

Keywords

Crossrefs

Programs

Formula

E.g.f.(x) for b(n) = n^(n-4) = a(n-4): T - (7/8)*T^2 + (11/36)*T^3 - (1/24)*T^4, where T = T(x) is Euler's tree function (see A000169). - Len Smiley, Nov 17 2001
E.g.f.: LambertW(-x)^4/(x^4*(1+LambertW(-x))). - Vladeta Jovovic, Nov 07 2003
E.g.f.: (1/3)*d/dx(LambertW(-x)/(-x))^3. - Wolfdieter Lang, Oct 25 2022

A008788 a(n) = n^(n+2).

Original entry on oeis.org

0, 1, 16, 243, 4096, 78125, 1679616, 40353607, 1073741824, 31381059609, 1000000000000, 34522712143931, 1283918464548864, 51185893014090757, 2177953337809371136, 98526125335693359375, 4722366482869645213696
Offset: 0

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Author

Keywords

Examples

			G.f. = x + 16*x^2 + 243*x^3 + 4096*x^4 + 78125*x^5 + 1679616*x^6 + ...
		

Crossrefs

Programs

Formula

E.g.f.(x): T*(1 + 2*T)*(1-T)^(-5); where T=T(x) is Euler's tree function (see A000169). - Len Smiley, Nov 17 2001
See A008517 and A134991 for similar e.g.f.s. and A048993. - Tom Copeland, Oct 03 2011
E.g.f.: d^2/dx^2 {x^2/(T(x)^2*(1-T(x)))}, where T(x) = Sum_{n>=1} n^(n-1)*x^n/n! is the tree function of A000169. - Peter Bala, Aug 05 2012

A048888 a(n) = Sum_{m=1..n} T(m,n+1-m), array T as in A048887.

Original entry on oeis.org

0, 1, 2, 4, 7, 13, 23, 42, 76, 139, 255, 471, 873, 1627, 3044, 5718, 10779, 20387, 38673, 73561, 140267, 268065, 513349, 984910, 1892874, 3643569, 7023561, 13557019, 26200181, 50691977, 98182665, 190353369, 369393465, 717457655
Offset: 0

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Author

Keywords

Comments

From Marc LeBrun, Dec 12 2001: (Start)
Define a "numbral arithmetic" by replacing addition with binary bitwise inclusive-OR (so that [3] + [5] = [7] etc.) and multiplication becomes shift-&-OR instead of shift-&-add (so that [3] * [3] = [7] etc.). [d] divides [n] means there exists an [e] with [d] * [e] = [n]. For example the six divisors of [14] are [1], [2], [3], [6], [7] and [14]. Then it appears that this sequence gives the number of proper divisors of [2^n-1]. Conjecture confirmed by Richard C. Schroeppel, Dec 14 2001. (End)
The number of "prime endofunctions" on n points, meaning the cardinality of the subset of the A001372(n) mappings (or mapping patterns) up to isomorphism from n (unlabeled) points to themselves (endofunctions) which are neither the sum of prime endofunctions (i.e., whose disjoint connected components are prime endofunctions) nor the categorical product of prime endofunctions. The n for which a(n) is prime (n such that the number of prime endofunctions on n points is itself prime) are 2, 4, 5, 6, 9, 13, 19, ... - Jonathan Vos Post, Nov 19 2006
For n>=1, compositions p(1)+p(2)+...+p(m)=n such that p(k)<=p(1)+1, see example. - Joerg Arndt, Dec 28 2012

Examples

			From _Joerg Arndt_, Dec 28 2012: (Start)
There are a(6)=23 compositions p(1)+p(2)+...+p(m)=6 such that p(k)<=p(1)+1:
[ 1]  [ 1 1 1 1 1 1 ]
[ 2]  [ 1 1 1 1 2 ]
[ 3]  [ 1 1 1 2 1 ]
[ 4]  [ 1 1 2 1 1 ]
[ 5]  [ 1 1 2 2 ]
[ 6]  [ 1 2 1 1 1 ]
[ 7]  [ 1 2 1 2 ]
[ 8]  [ 1 2 2 1 ]
[ 9]  [ 2 1 1 1 1 ]
[10]  [ 2 1 1 2 ]
[11]  [ 2 1 2 1 ]
[12]  [ 2 1 3 ]
[13]  [ 2 2 1 1 ]
[14]  [ 2 2 2 ]
[15]  [ 2 3 1 ]
[16]  [ 3 1 1 1 ]
[17]  [ 3 1 2 ]
[18]  [ 3 2 1 ]
[19]  [ 3 3 ]
[20]  [ 4 1 1 ]
[21]  [ 4 2 ]
[22]  [ 5 1 ]
[23]  [ 6 ]
(End)
		

Crossrefs

Programs

  • PARI
    N = 66;  x = 'x + O('x^N);
    gf = sum(n=0,N,  (1-x^n)*x^n/(1-2*x+x^(n+1)) ) + 'c0;
    v = Vec(gf);  v[1]-='c0;  v
    /* Joerg Arndt, Apr 14 2013 */

Formula

G.f.: Sum_{k>0} x^k*(1-x^k)/(1-2*x+x^(k+1)). - Vladeta Jovovic, Feb 25 2003
a(m) = Sum_{ n=2..m+1 } Fn(m) where Fn is a Fibonacci n-step number (Fibonacci, tetranacci, etc.) indexed as in A000045, A000073, A000078. - Gerald McGarvey, Sep 25 2004

A056849 Final digit of n^n.

Original entry on oeis.org

1, 4, 7, 6, 5, 6, 3, 6, 9, 0, 1, 6, 3, 6, 5, 6, 7, 4, 9, 0, 1, 4, 7, 6, 5, 6, 3, 6, 9, 0, 1, 6, 3, 6, 5, 6, 7, 4, 9, 0, 1, 4, 7, 6, 5, 6, 3, 6, 9, 0, 1, 6, 3, 6, 5, 6, 7, 4, 9, 0, 1, 4, 7, 6, 5, 6, 3, 6, 9, 0, 1, 6, 3, 6, 5, 6, 7, 4, 9, 0, 1, 4, 7, 6, 5, 6, 3, 6, 9, 0, 1, 6, 3, 6, 5, 6, 7, 4, 9, 0
Offset: 1

Views

Author

Robert G. Wilson v, Aug 30 2000

Keywords

Comments

Cyclic with a period of 20.
Also decimal expansion of 147656369016365674900/(10^20-1). - Bruno Berselli, Sep 27 2021

References

  • R. Euler and J. Sadek, "A Number That Gives The Units Of n^n", Journal of Recreational Mathematics, vol. 29(3), 1998, pp. 203-4.

Crossrefs

Programs

  • Magma
    [Modexp(n, n, 10): n in [1..100]]; // Bruno Berselli, Sep 27 2021
    
  • Maple
    seq(n &^ n mod 10, n=1..120);
  • Mathematica
    Table[PowerMod[n, n, 10], {n, 1, 100}]
  • PARI
    a(n)=lift(Mod(n,10)^n) \\ Charles R Greathouse IV, Dec 29 2012
    
  • Python
    def a(n): return pow(n, n, 10)
    print([a(n) for n in range(1, 101)]) # Michael S. Branicky, Sep 13 2022

A130293 Number of necklaces of n beads with up to n colors, with cyclic permutation {1,..,n} of the colors taken to be equivalent.

Original entry on oeis.org

1, 2, 5, 20, 129, 1316, 16813, 262284, 4783029, 100002024, 2357947701, 61917406672, 1792160394049, 56693913450992, 1946195068379933, 72057594071484456, 2862423051509815809, 121439531097819321972, 5480386857784802185957, 262144000000051200072048, 13248496640331026150086281
Offset: 1

Views

Author

Wouter Meeussen, Aug 06 2007, Aug 14 2007

Keywords

Comments

From Olivier Gérard, Aug 01 2016: (Start)
Equivalent to the definition: number of classes of endofunctions of [n] under rotation and translation mod n.
Classes can be of size between n and n^2 depending on divisibility properties of n.
n n 2n 3n ... n^2
--------------------------
1 1
2 2
3 3 2
4 4 2 14
5 5 0 124
6 6 6 22 1282
7 7 0 16806
For prime n, the only possible class sizes are n and n^2, the classes of size n are the n arithmetical progression modulo n so #(c-n)=n, #(c-n^2)=(n^n - n*n)/n^2 = n^(n-2)-1 and a(n) = n^(n-2)+n-1.
(End)

Examples

			The 5 necklaces for n=3 are: 000, 001, 002, 012 and 021.
		

Crossrefs

Cf. A081720.
Cf. A000312: All endofunctions.
Cf. A000169: Classes under translation mod n.
Cf. A001700: Classes under sort.
Cf. A056665: Classes under rotation.
Cf. A168658: Classes under complement to n+1.
Cf. A130293: Classes under translation and rotation.
Cf. A081721: Classes under rotation and reversal.
Cf. A275549: Classes under reversal.
Cf. A275550: Classes under reversal and complement.
Cf. A275551: Classes under translation and reversal.
Cf. A275552: Classes under translation and complement.
Cf. A275553: Classes under translation, complement and reversal.
Cf. A275554: Classes under translation, rotation and complement.
Cf. A275555: Classes under translation, rotation and reversal.
Cf. A275556: Classes under translation, rotation, complement and reversal.
Cf. A275557: Classes under rotation and complement.
Cf. A275558: Classes under rotation, complement and reversal.

Programs

  • Mathematica
    tor8={};ru8=Thread[ i_ ->Table[ Mod[i+k,8],{k,8}]];Do[idi=IntegerDigits[k,8,8];try= Function[w, First[temp=Union[Join @@(Table[RotateRight[w,k],{k,8}]/.#&)/@ ru8]]][idi];If[idi===try, tor8=Flatten[ {tor8,{{Length[temp],idi}}},1] ],{k,0,8^8-1}];
    a[n_]:=Sum[d EulerPhi[d]n^(n/d),{d,Divisors[n]}]/n^2; Array[a,21] (* Stefano Spezia, May 21 2024 *)
  • PARI
    a(n) = sumdiv(n, d, d*eulerphi(d)*n^(n/d))/n^2; \\ Michel Marcus, Aug 05 2016

Formula

a(n) = (1/n^2)*Sum_{d|n} d*phi(d)*n^(n/d). - Vladeta Jovovic, Aug 14 2007, Aug 24 2007

A155955 Triangle read by rows: T(n,k) = (k*n)^k, 0 <= k <= n.

Original entry on oeis.org

1, 1, 1, 1, 2, 16, 1, 3, 36, 729, 1, 4, 64, 1728, 65536, 1, 5, 100, 3375, 160000, 9765625, 1, 6, 144, 5832, 331776, 24300000, 2176782336, 1, 7, 196, 9261, 614656, 52521875, 5489031744, 678223072849, 1, 8, 256, 13824, 1048576, 102400000, 12230590464
Offset: 0

Views

Author

Reinhard Zumkeller, Jan 31 2009

Keywords

Comments

T(n,0) = 1;
T(n,1) = n for n > 0;
T(n,2) = A016742(n) for n > 1;
T(n,3) = A016767(n) for n > 2;
T(n,4) = A016804(n) for n > 3;
T(n,5) = A016853(n) for n > 4;
T(n,6) = A016914(n) for n > 5;
T(n,7) = A016987(n) for n > 6;
T(n,8) = A017072(n) for n > 7;
T(n,9) = A017169(n) for n > 8;
T(n,10) = A017278(n) for n > 9;
T(n,11) = A017399(n) for n > 10;
T(n,12) = A017532(n) for n > 11;
T(n,n) = A062206(n).

Examples

			Triangle begins:
  1;
  1, 1;
  1, 2,  16;
  1, 3,  36,  729;
  1, 4,  64, 1728,  65536;
  1, 5, 100, 3375, 160000,  9765625;
  1, 6, 144, 5832, 331776, 24300000, 2176782336;
  ...
		

Crossrefs

Cf. A000312.

Programs

  • Magma
    [[(n*k)^k: k in [0..n]]: n in [0..10]]; // G. C. Greubel, Sep 15 2018
  • Mathematica
    Table[If[n == 0, 1, If[ k == 0, 1, (k*n)^k]], {n, 0, 10}, {k, 0, n}]//Flatten (* G. C. Greubel, Sep 15 2018 *)
  • PARI
    for(n=0,10, for(k=0,n, print1((k*n)^k, ", "))) \\ G. C. Greubel, Sep 15 2018
    

A222029 Triangle of number of functions in a size n set for which the sequence of composition powers ends in a length k cycle.

Original entry on oeis.org

1, 1, 3, 1, 16, 9, 2, 125, 93, 32, 6, 1296, 1155, 480, 150, 24, 20, 16807, 17025, 7880, 3240, 864, 840, 262144, 292383, 145320, 71610, 24192, 26250, 720, 0, 0, 504, 0, 420, 4782969, 5752131, 3009888, 1692180, 653184, 773920, 46080, 5040, 0, 32256, 0, 26880, 0, 0, 2688
Offset: 0

Views

Author

Chad Brewbaker, May 14 2013

Keywords

Comments

If you take the powers of a finite function you generate a lollipop graph. This table organizes the lollipops by cycle size. The table organized by total lollipop size with the tail included is A225725.
Warning: For T(n,k) after the sixth row there are zero entries and k can be greater than n: T(7,k) = |{1=>262144, 2=>292383, 3=>145320, 4=>71610, 5=>24192, 6=>26250, 7=>720, 8=>0, 9=>0, 10=>504, 11=>0, 12=>420}|.

Examples

			T(1,1) = |{[0]}|, T(2,1) = |{[0,0],[0,1],[1,1]}|, T(2,2) = |{[0,1]}|.
Triangle starts:
       1;
       1;
       3,      1;
      16,      9,      2;
     125,     93,     32,     6;
    1296,   1155,    480,   150,    24,    20;
   16807,  17025,   7880,  3240,   864,   840;
  262144, 292383, 145320, 71610, 24192, 26250, 720, 0, 0, 504, 0, 420;
  ...
		

Crossrefs

Rows sums give A000312.
Row lengths are A000793.
Number of nonzero elements of rows give A009490.
Last elements of rows give A162682.
Main diagonal gives A290961.
Cf. A057731 (the same for permutations), A290932.

Programs

  • Maple
    b:= proc(n, m) option remember; `if`(n=0, x^m, add((j-1)!*
          b(n-j, ilcm(m, j))*binomial(n-1, j-1), j=1..n))
        end:
    T:= n-> (p-> seq(coeff(p, x, i), i=1..degree(p)))(add(
             b(j, 1)*n^(n-j)*binomial(n-1, j-1), j=0..n)):
    seq(T(n), n=0..10);  # Alois P. Heinz, Aug 14 2017
  • Mathematica
    b[n_, m_]:=b[n, m]=If[n==0, x^m, Sum[(j - 1)!*b[n - j, LCM[m, j]] Binomial[n - 1, j - 1], {j, n}]]; T[n_]:=If[n==0, {1}, Drop[CoefficientList[Sum[b[j, 1]n^(n - j)*Binomial[n - 1, j - 1], {j, 0, n}], x], 1]]; Table[T[n], {n, 0, 10}]//Flatten (* Indranil Ghosh, Aug 17 2017 *)
  • Python
    from sympy.core.cache import cacheit
    from sympy import binomial, Symbol, lcm, factorial as f, Poly, flatten
    x=Symbol('x')
    @cacheit
    def b(n, m): return x**m if n==0 else sum([f(j - 1)*b(n - j, lcm(m, j))*binomial(n - 1, j - 1) for j in range(1, n + 1)])
    def T(n): return Poly(sum([b(j, 1)*n**(n - j)*binomial(n - 1, j - 1) for j in range(n + 1)]),x).all_coeffs()[::-1][1:]
    print([T(n) for n in range(11)]) # Indranil Ghosh, Aug 17 2017

Formula

Sum_{k=1..A000793(n)} k * T(n,k) = A290932. - Alois P. Heinz, Aug 14 2017

Extensions

T(0,1)=1 prepended by Alois P. Heinz, Aug 14 2017
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