A000169 -id:A000169 - cp's OEIS frontend

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

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

Offset: 0

N. J. A. Sloane

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Cf. A000169, A000272, A000312, A007778, A007830, A008786, A008787, A008788, A008789, A008790, A008791.

List([0..20], n-> (n+4)^n); # G. C. Greubel, Sep 11 2019

[(n+4)^n: n in [0..20]]; // Vincenzo Librandi, Jun 11 2013

Table[(n+4)^n,{n,0,20}] (* Vladimir Joseph Stephan Orlovsky, Dec 26 2010 *)

vector(20, n, (n+3)^(n-1)) \\ G. C. Greubel, Nov 09 2017

[(n+4)^n for n in (0..20)] # G. C. Greubel, Sep 11 2019

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

N. J. A. Sloane

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

Vincenzo Librandi, Table of n, a(n) for n = 0..200
Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

Cf. A000169, A000272, A000312, A007778, A007830, A008785, A008786, A008787, A008789, A008790, A008791.

List([0..20], n-> n^(n+2)); # G. C. Greubel, Sep 11 2019

[n^(n+2): n in [0..20]]; // Vincenzo Librandi, Jun 11 2013

Table[n^(n+2), {n,0,20}] (* Vladimir Joseph Stephan Orlovsky, Dec 26 2010 *)
CoefficientList[Series[LambertW[-x] * (2*LambertW[-x]-1) / (1 + LambertW[-x])^5, {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Dec 20 2014 *)

vector(20, n, (n-1)^(n+1)) \\ G. C. Greubel, Nov 14 2017

[n^(n+2) for n in (0..20)] # G. C. Greubel, Sep 11 2019

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

A053507 a(n) = binomial(n-1,2)*n^(n-3).

Original entry on oeis.org

0, 0, 1, 12, 150, 2160, 36015, 688128, 14880348, 360000000, 9646149645, 283787919360, 9098660462034, 315866083233792, 11806916748046875, 472877960873902080, 20205339187128111480, 917543123840934346752, 44131536275846038655193

Offset: 1

N. J. A. Sloane, Jan 15 2000

Number of connected unicyclic simple graphs on n labeled nodes such that the unique cycle has length 3. - Len Smiley, Nov 27 2001

Each simple graph (of this type) corresponds to exactly two 'functional digraphs' counted by A065513.

R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Prop. 5.3.2.

Vincenzo Librandi, Table of n, a(n) for n = 1..100

Cf. A000169, A053506, A053508, A053509, A081133, A081132.

Equals 2*A065513. A diagonal of A081130.

List([1..20], n-> Binomial(n-1,2)*n^(n-3)); # G. C. Greubel, May 15 2019

[Binomial(n-1,2)*n^(n-3):n in [1..20]]; // Vincenzo Librandi, Sep 22 2011

[Binomial(n-1,2)*n^(n-3): n in [1..20]]; // G. C. Greubel, May 15 2019

nn = 20; t = Sum[n^(n - 1) x^n/n!, {n, 1, nn}]; Rest[Range[0, nn]! CoefficientList[Series[t^3/3!, {x, 0, nn}], x]] (* Geoffrey Critzer, Jan 22 2012 *)
Table[Binomial[n-1,2]n^(n-3),{n,20}] (* Harvey P. Dale, Sep 24 2019 *)

vector(20, n, binomial(n-1,2)*n^(n-3)) \\ G. C. Greubel, Jan 18 2017

[binomial(n-1,2)*n^(n-3) for n in (1..20)] # G. C. Greubel, May 15 2019

E.g.f.: -LambertW(-x)^3/3!. - Vladeta Jovovic, Apr 07 2001

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

Wouter Meeussen, Aug 06 2007, Aug 14 2007

nonn

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)

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

Stefano Spezia, Table of n, a(n) for n = 1..350
Darij Grinberg and Peter Mao, Necklaces over a group with identity product, arXiv:2405.08937 [math.CO], 2024. See p. 22.

Cf. A002075-A002076.
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.

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 *)

a(n) = sumdiv(n, d, d*eulerphi(d)*n^(n/d))/n^2; \\ Michel Marcus, Aug 05 2016

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

A216857 Number of connected functions from {1,2,...,n} into a subset of {1,2,...,n} that have a fixed point summed over all subsets.

Original entry on oeis.org

0, 1, 4, 24, 224, 2880, 47232, 942592, 22171648, 600698880, 18422374400, 630897721344, 23864653578240, 988197253808128, 44460603225407488, 2159714024218951680, 112652924603290615808, 6280048587936003784704, 372616014329572403183616, 23445082059018189741752320, 1559275240299007139066675200

Offset: 0

Geoffrey Critzer, Sep 17 2012

nonn

Essentially the same as A038049.
Also the number of rooted trees whose nodes are labeled with the blocks of a set partition of {1,2,...,n} each having a distinguished element. (See A000248.)
The bijection is straightforward. The trees correspond to functional digraphs mapping the distinguished elements towards the root. All the elements within each block are mapped to the distinguished element of that block. The distinguished element in the root node is the fixed point.

Vincenzo Librandi, Table of n, a(n) for n = 0..200
Alexander Burstein and Louis W. Shapiro, Pseudo-involutions in the Riordan group, arXiv:2112.11595 [math.CO], 2021.

Cf. A048802, A072034.

With[{nmax = 20}, CoefficientList[Series[-LambertW[-x*Exp[x]], {x, 0, nmax}], x]*Range[0, nmax]!] (* modified by G. C. Greubel, Nov 15 2017 *)

for(n=0,30, print1(sum(k=1,n, binomial(n,k)*k^(n-1)), ", ")) \\ G. C. Greubel, Nov 15 2017

my(x='x+O('x^50)); concat([0], Vec(serlaplace(-lambertw(-x*exp(x))))) \\ G. C. Greubel, Nov 15 2017

E.g.f.: T(x*exp(x)) where T(x) is the e.g.f. for A000169.
a(n) = Sum_{k=1..n} binomial(n,k)*k^(n-1).
a(n) ~ sqrt(1+LambertW(exp(-1))) * n^(n-1) / (exp(n)*LambertW(exp(-1))^n). - Vaclav Kotesovec, Jul 09 2013
O.g.f.: Sum_{n>=0} n^(n-1)* x^n / (1 - n*x)^(n+1). - Paul D. Hanna, May 22 2018
E.g.f.: the compositional inverse of A(x) is -A(-x). - Alexander Burstein, Aug 11 2018

A275558 Number of classes of endofunctions of [n] under rotation, complement to n+1 and reversal.

Original entry on oeis.org

1, 1, 2, 6, 31, 195, 2182, 30100, 529674, 10778125, 250155012, 6484839306, 185757443582, 5824538174455, 198428907905336, 7298232189810696, 288230385949610020, 12165298000307625609, 546477890436083284338, 26031837576091248872110, 1310720000028416000168044

Offset: 0

Olivier Gérard, Aug 05 2016

nonn

Classes can be of size 1,2,4, n, 2n or 4n.
.
n   1  2  4      n     2n     4n
---------------------------------
1   1
2   0  2
3   1  1                4
4   0  4  4      0     17      6
5   1  2  0      0     72    120
6   0  6  6     30    410   1730
7   1  3  0      0   1368  28728
.
For n odd, the constant function (n+1)/2 is the only stable by rotation, complement and reversal. So #c1=1.
For n even, there is no stable function, so #c1=0, but constant functions are grouped two by two making n/2 classes of size 2. Functions alternating a value and its complement are also grouped two by two, making another n/2 classes. This gives #c2=n.

Andrew Howroyd, Table of n, a(n) for n = 0..100

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

\\ see A056391 for Polya enumeration functions
a(n) = NonequivalentSorts(DihedralPerms(n), ReversiblePerms(n)); \\ Andrew Howroyd, Sep 30 2017

Terms a(8) and beyond from Andrew Howroyd, Sep 30 2017

A369140 Number of labeled loop-graphs covering {1..n} such that it is possible to choose a different vertex from each edge (choosable).

Original entry on oeis.org

1, 1, 4, 23, 193, 2133, 29410, 486602, 9395315, 207341153, 5147194204, 141939786588, 4304047703755, 142317774817901, 5095781837539766, 196403997108015332, 8106948166404074281, 356781439557643998591, 16675999433772328981216, 824952192369049982670686

Offset: 0

Gus Wiseman, Jan 20 2024

nonn

These are covering loop-graphs where every connected component has a number of edges less than or equal to the number of vertices in that component. Also covering loop-graphs with at most one cycle (unicyclic) in each connected component.

			The a(0) = 1 through a(3) = 23 loop-graphs (loops shown as singletons):
  {}  {{1}}  {{1,2}}      {{1},{2,3}}
             {{1},{2}}    {{2},{1,3}}
             {{1},{1,2}}  {{3},{1,2}}
             {{2},{1,2}}  {{1,2},{1,3}}
                          {{1,2},{2,3}}
                          {{1},{2},{3}}
                          {{1,3},{2,3}}
                          {{1},{2},{1,3}}
                          {{1},{2},{2,3}}
                          {{1},{3},{1,2}}
                          {{1},{3},{2,3}}
                          {{2},{3},{1,2}}
                          {{2},{3},{1,3}}
                          {{1},{1,2},{1,3}}
                          {{1},{1,2},{2,3}}
                          {{1},{1,3},{2,3}}
                          {{2},{1,2},{1,3}}
                          {{2},{1,2},{2,3}}
                          {{2},{1,3},{2,3}}
                          {{3},{1,2},{1,3}}
                          {{3},{1,2},{2,3}}
                          {{3},{1,3},{2,3}}
                          {{1,2},{1,3},{2,3}}

Andrew Howroyd, Table of n, a(n) for n = 0..200

For a unique choice we have A000272, covering case of A088957.
Without the choice condition we have A322661, unlabeled A322700.
For exactly n edges we have A333331 (maybe), complement A368596.
The case without loops is A367869, covering case of A133686.
This is the covering case of A368927.
The complement is counted by A369142, covering case of A369141.
The unlabeled version is the first differences of A369145.
A000085, A100861, A111924 count set partitions into singletons or pairs.
A006125 counts simple graphs; also loop-graphs if shifted left.
A006129 counts covering graphs, unlabeled A002494.
A054548 counts graphs covering n vertices with k edges, with loops A369199.
A367862 counts graphs with n vertices and n edges, covering A367863.
Cf. A000169, A000666, A003465, A006649, A062740, A116508, A137916, A368924, A368984, A369194.

Table[Length[Select[Subsets[Subsets[Range[n], {1,2}]],Union@@#==Range[n]&&Length[Select[Tuples[#], UnsameQ@@#&]]!=0&]],{n,0,5}]

seq(n)={my(t=-lambertw(-x + O(x*x^n))); Vec(serlaplace(exp(-x + 3*t/2 - 3*t^2/4)/sqrt(1-t) ))} \\ Andrew Howroyd, Feb 02 2024

Inverse binomial transform of A368927.
Exponential transform of A369197.
E.g.f.: exp(-x)*exp(3*T(x)/2 - 3*T(x)^2/4)/sqrt(1-T(x)), where T(x) is the e.g.f. of A000169. - Andrew Howroyd, Feb 02 2024

a(6) onwards from Andrew Howroyd, Feb 02 2024

A369191 Number of labeled simple graphs covering n vertices with at most n edges.

Original entry on oeis.org

1, 0, 1, 4, 34, 387, 5686, 102084, 2162168, 52693975, 1450876804, 44509105965, 1504709144203, 55563209785167, 2224667253972242, 95984473918245388, 4439157388017620554, 219067678811211857307, 11489425098298623161164, 638159082104453330569185

Offset: 0

Gus Wiseman, Jan 17 2024

nonn

Row-sums of left portion of A054548.

			The a(0) = 1 through a(3) = 4 graphs:
  {}  .  {{1,2}}  {{1,2},{1,3}}
                  {{1,2},{2,3}}
                  {{1,3},{2,3}}
                  {{1,2},{1,3},{2,3}}

The minimal case is A053530.
The connected case is A129271, unlabeled version A005703.
The case of equality is A367863, covering case of A367862.
This is the covering case of A369192, or A369193 for covered vertices.
The version for loop-graphs is A369194.
The unlabeled version is A370316.
A001187 counts connected graphs, unlabeled A001349.
A006125 counts graphs, unlabeled A000088.
A006129 counts covering graphs, unlabeled A002494.
A054548 counts graphs covering n vertices with k edges, with loops A369199.
A057500 counts connected graphs with n vertices and n edges.
A133686 counts choosable graphs, covering A367869.
A367867 counts non-choosable graphs, covering A367868.
Cf. A000169, A000272, A000666, A001429, A003465, A006649, A143543, A116508, A140638, A322661.

Table[Length[Select[Subsets[Subsets[Range[n], {2}]],Length[Union@@#]==n&&Length[#]<=n&]],{n,0,5}]

Inverse binomial transform of A369193.

A008791 a(n) = n^(n+5).

Original entry on oeis.org

0, 1, 128, 6561, 262144, 9765625, 362797056, 13841287201, 549755813888, 22876792454961, 1000000000000000, 45949729863572161, 2218611106740436992, 112455406951957393129, 5976303958948914397184, 332525673007965087890625

Offset: 0

N. J. A. Sloane

Vincenzo Librandi, Table of n, a(n) for n = 0..200
Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets

Cf. A000169, A000272, A000312, A007778, A007830, A008785, A008786, A008787, A008788, A008789, A008790.

List([0..20], n-> n^(n+5)); # G. C. Greubel, Sep 11 2019

[n^(n+5): n in [0..20]]; // Vincenzo Librandi, Jun 11 2013

a:=n->mul( n, k=-4..n): seq(a(n), n=0..20); # Zerinvary Lajos, Jan 26 2008

Table[n^(n+5),{n,0,20}] (* Vladimir Joseph Stephan Orlovsky, Dec 26 2010 *)

vector(20, n, (n-1)^(n+4)) \\ G. C. Greubel, Sep 11 2019

[n^(n+5) for n in (0..20)] # G. C. Greubel, Sep 11 2019

E.g.f.(x): T*(1 + 52*T + 328*T^2 + 444*T^3 + 120*T^4)*(1-T)^(-11); 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 diagonals of A048993. - Tom Copeland, Oct 03 2011
E.g.f.: d^5/dx^5 {x^5/(T(x)^5*(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

A036878 a(n) = p^(p-1) where p = prime(n).

Original entry on oeis.org

2, 9, 625, 117649, 25937424601, 23298085122481, 48661191875666868481, 104127350297911241532841, 907846434775996175406740561329, 88540901833145211536614766025207452637361, 550618520345910837374536871905139185678862401

Offset: 1

Simon Colton (simonco(AT)cs.york.ac.uk)

Also the least refactorable number (A033950) that has the n-th prime as its least prime factor. - Robert G. Wilson v, Jun 28 2006

			5^(5-1) = 5^4 = 625.

Vincenzo Librandi, Table of n, a(n) for n = 1..77
S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2.
S. Colton, HR - Automatic Theory Formation in Pure Mathematics

These integers are refactorable -- i.e., the number of divisors divides the number itself, cf. A033950.
Subset of A062981. Subsequence of A000169.
Subsequence of A111134 and A246655.

[p^(p-1): p in PrimesUpTo(50)]; // Vincenzo Librandi, Mar 27 2014

Table[Prime@n^(Prime@n - 1), {n, 10}] (* Robert G. Wilson v, Jun 28 2006 *)
#^(#-1)&/@Prime[Range[10]] (* Harvey P. Dale, Oct 23 2015 *)

a(n) = my(p=prime(n)); p^(p-1); \\ Michel Marcus, Jan 24 2019

cp's OEIS Frontend

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

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

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A053507 a(n) = binomial(n-1,2)*n^(n-3).

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

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A216857 Number of connected functions from {1,2,...,n} into a subset of {1,2,...,n} that have a fixed point summed over all subsets.

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A275558 Number of classes of endofunctions of [n] under rotation, complement to n+1 and reversal.

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A369140 Number of labeled loop-graphs covering {1..n} such that it is possible to choose a different vertex from each edge (choosable).

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