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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A007781 a(n) = (n+1)^(n+1) - n^n for n>0, a(0) = 1.

Original entry on oeis.org

1, 3, 23, 229, 2869, 43531, 776887, 15953673, 370643273, 9612579511, 275311670611, 8630788777645, 293959006143997, 10809131718965763, 426781883555301359, 18008850183328692241, 808793517812627212561
Offset: 0

Views

Author

Peter McCormack (peter.mccormack(AT)its.csiro.au)

Keywords

Comments

(12n^2 + 6n + 1)^2 divides a(6n+1), where (12n^2 + 6n + 1) = (2n+1)^3 - (2n)^3 = A127854(n) = A003215(2n) are the hex (or centered hexagonal) numbers. The prime numbers of the form 12n^2 + 6n + 1 belong to A002407. - Alexander Adamchuk, Apr 09 2007

Examples

			a(14) = 10809131718965763 = 3 * 61^2 * 968299894201.
		

References

  • Richard P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see equation (6.7).

Crossrefs

Programs

Formula

a(n) = A000312(n+1) - A000312(n) for n>0, a(0) = 1.
a(n) = abs(discriminant(x^(n+1)-x+1)).
E.g.f.: W(-x)/(1+W(-x)) - W(-x)/((1+W(-x))^3*x) where W is the Lambert W function. - Robert Israel, Aug 19 2015
Limit_{n->oo} (a(n+2)/a(n+1) - a(n+1)/a(n)) = e (Cusumano, 2007). - Amiram Eldar, Jan 03 2022

A066068 a(n) = n^n + n.

Original entry on oeis.org

1, 2, 6, 30, 260, 3130, 46662, 823550, 16777224, 387420498, 10000000010, 285311670622, 8916100448268, 302875106592266, 11112006825558030, 437893890380859390, 18446744073709551632, 827240261886336764194
Offset: 0

Views

Author

George E. Antoniou, Dec 02 2001

Keywords

Crossrefs

Programs

Formula

E.g.f.: (1-x*e^x*T(x)+x*e^x)/(1-T(x)), where T(x) is Euler's tree function (see A000169). - Len Smiley, Dec 04 2001
Resultant of nx^n+1 and nx-1. - Ralf Stephan, Nov 20 2004
a(n) = n*A124923(n), n>0. - R. J. Mathar, Oct 31 2015
Sum_{n>=1} 1/a(n) = A286193. - Amiram Eldar, Nov 19 2020

A241981 Number T(n,k) of endofunctions on [n] where the largest cycle length equals 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, 16, 9, 2, 0, 125, 93, 32, 6, 0, 1296, 1155, 500, 150, 24, 0, 16807, 17025, 8600, 3240, 864, 120, 0, 262144, 292383, 165690, 72030, 24696, 5880, 720, 0, 4782969, 5752131, 3568768, 1719060, 688128, 215040, 46080, 5040
Offset: 0

Views

Author

Alois P. Heinz, Aug 10 2014

Keywords

Comments

T(0,0) = 1 by convention.
In general, number of endofunctions on [n] where the largest cycle length equals k is asymptotic to (k*exp(H(k)) - (k-1)*exp(H(k-1))) * n^(n-1), where H(k) is the harmonic number A001008/A002805, k>=1. The multiplicative constant is (for big k) asymptotic to 2*k*exp(gamma), where gamma is the Euler-Mascheroni constant (see A001620 and A073004). - Vaclav Kotesovec, Aug 21 2014

Examples

			Triangle T(n,k) begins:
  1;
  0,      1;
  0,      3,      1;
  0,     16,      9,      2;
  0,    125,     93,     32,     6;
  0,   1296,   1155,    500,   150,    24;
  0,  16807,  17025,   8600,  3240,   864,  120;
  0, 262144, 292383, 165690, 72030, 24696, 5880, 720;
  ...
		

Crossrefs

Columns k=0-10 give: A000007, A000272(n+1) for n>0, A163951, A246213, A246214, A246215, A246216, A246217, A246218, A246219, A246220.
T(2n,n) gives A241982.
Row sums give A000312.
Main diagonal gives A000142(n-1) for n>0.

Programs

  • Maple
    with(combinat):
    b:= proc(n, i) option remember; `if`(n=0, 1, `if`(i<1, 0,
          add((i-1)!^j*multinomial(n, n-i*j, i$j)/j!*
          b(n-i*j, i-1), j=0..n/i)))
        end:
    A:= (n, k)-> add(binomial(n-1, j-1)*n^(n-j)*b(j, min(j, k)), j=0..n):
    T:= (n, k)-> A(n, k) -`if`(k=0, 0, A(n, k-1)):
    seq(seq(T(n, k), k=0..n), n=0..10);
  • Mathematica
    multinomial[n_, k_List] := n!/Times @@ (k!); b[n_, i_] := b[n, i] = If[n == 0, 1, If[i<1, 0, Sum[(i-1)!^j*multinomial[n, {n-i*j, Sequence @@ Table[i, {j}]}]/j!*b[n-i*j, i-1], {j, 0, n/i}]]]; A[n_, k_] := Sum[Binomial[n-1, j-1]*n^(n-j)*b[j, Min[j, k]], {j, 0, n}]; T[0, 0] = 1; T[n_, k_] := A[n, k] - If[k == 0, 0, A[n, k-1]]; Table[Table[T[n, k], {k, 0, n}], {n, 0, 10}] // Flatten (* Jean-François Alcover, Jan 06 2015, after Alois P. Heinz *)

A245733 Number T(n,k) of endofunctions on [n] such that at least one preimage with cardinality k exists and, if j is the largest value with a nonempty preimage, the preimage cardinality of i is >=k for all i<=j and equal to k for at least one i<=j; triangle T(n,k), n>=0, 0<=k<=n, read by rows.

Original entry on oeis.org

1, 0, 1, 1, 2, 1, 14, 12, 0, 1, 181, 68, 6, 0, 1, 2584, 520, 20, 0, 0, 1, 41973, 4542, 120, 20, 0, 0, 1, 776250, 46550, 672, 70, 0, 0, 0, 1, 16231381, 540136, 5516, 112, 70, 0, 0, 0, 1, 380333228, 7045020, 40140, 1848, 252, 0, 0, 0, 0, 1
Offset: 0

Views

Author

Alois P. Heinz, Jul 30 2014

Keywords

Comments

T(0,0) = 1 by convention.

Examples

			T(2,0) = 1: (2,2).
T(2,1) = 2: (1,2), (2,1).
T(2,2) = 1: (1,1).
T(3,1) = 12: (1,1,2), (1,2,1), (1,2,2), (1,2,3), (1,3,2), (2,1,1), (2,1,2), (2,1,3), (2,2,1), (2,3,1), (3,1,2), (3,2,1).
T(3,3) = 1: (1,1,1).
Triangle T(n,k) begins:
0 :         1;
1 :         0,      1;
2 :         1,      2,    1;
3 :        14,     12,    0,   1;
4 :       181,     68,    6,   0,  1;
5 :      2584,    520,   20,   0,  0, 1;
6 :     41973,   4542,  120,  20,  0, 0, 1;
7 :    776250,  46550,  672,  70,  0, 0, 0, 1;
8 :  16231381, 540136, 5516, 112, 70, 0, 0, 0, 1;
     ...
		

Crossrefs

Columns k=0-10 give: A133286 (for n>0), A245854, A245855, A245856, A245857, A245858, A245859, A245860, A245861, A245862, A245863.
Row sums give A000312.
T(2n,n) gives A000984(n).
Cf. A245732.

Programs

  • Maple
    b:= proc(n, k) option remember; `if`(n=0, 1,
          add(b(n-j, k)*binomial(n, j), j=k..n))
        end:
    g:= (n, k)-> `if`(k=0, n^n, `if`(n=0, 0, b(n, k))):
    T:= (n, k)-> g(n, k) -g(n, k+1):
    seq(seq(T(n, k), k=0..n), n=0..12);
  • Mathematica
    b[n_, k_] := b[n, k] = If[n == 0, 1, Sum[b[n-j, k]*Binomial[n, j], {j, k, n}]]; g[n_, k_] := If[k == 0, n^n, If[n == 0, 0, b[n, k]]]; T[n_, k_] := g[n, k] - g[n, k+1]; T[0, 0] = 1; Table[Table[T[n, k], {k, 0, n}], {n, 0, 12}] // Flatten (* Jean-François Alcover, Jan 27 2015, after Alois P. Heinz *)

Formula

E.g.f. of column k=0: 1 +1/(1+LambertW(-x)) -1/(2-exp(x)); e.g.f. of column k>0: 1/(1-Sum_{j>=k} x^j/j!) - 1/(1-Sum_{j>=k+1} x^j/j!).
T(n,k) = A245732(n,k) - A245732(n,k+1).

A275551 Number of classes of endofunctions of [n] under vertical translation mod n and reversal.

Original entry on oeis.org

1, 1, 2, 6, 36, 325, 3924, 58996, 1049088, 21526641, 500010000, 12968792826, 371504434176, 11649044974645, 396857394156608, 14596463098125000, 576460752571858944, 24330595941321312961, 1092955779880368226560, 52063675149116964615310, 2621440000000512000000000
Offset: 0

Views

Author

Olivier Gérard, Aug 02 2016

Keywords

Comments

There are two size of classes, n or 2n.
n c:n c:2n (c:n)/n (c:2n)/n
0 1
1 1
2 2
3 3 3 1 1
4 8 28 2 7
5 25 300 5 60
6 72 3852 12 642
7 343 58653 49 8379

Examples

			a(2) = 2: 11, 12.
a(3) = 6: 111, 112, 113, 121, 123, 131.
a(4) = 36: 1111, 1112, 1113, 1114, 1121, 1122, 1123, 1124, 1131, 1132, 1133, 1134, 1141, 1142, 1143, 1212, 1213, 1214, 1221, 1223, 1224, 1231, 1234, 1241, 1242, 1243, 1312, 1313, 1323, 1324, 1331, 1334, 1341, 1412, 1423, 1441.
		

Crossrefs

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. 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

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

Extensions

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

A275552 Number of classes of endofunctions of [n] under vertical translation mod n and complement to n+1.

Original entry on oeis.org

1, 1, 2, 5, 36, 313, 3904, 58825, 1048640, 21523361, 500000256, 12968712301, 371504186368, 11649042561241, 396857386631168, 14596463012695313, 576460752303439872, 24330595937833434241, 1092955779869348331520, 52063675148955620766421, 2621440000000000000262144
Offset: 0

Views

Author

Olivier Gérard, Aug 02 2016

Keywords

Comments

There are two size of classes, n or 2n.
.
n c:n c:2n (c:2n)/4
0 1
1 1
2 2
3 1 4 1
4 8 28 7
5 1 312 78
6 32 3872 968
7 1 58824 14706
For n odd, only the set of n constant functions can have a member of their class equal to their complement, so c:n size is 1.
For n even, the c:n class is populated by binary words using k for 0 and n+1-k for 1. There are (2^n)/2 such words as the complement operation identifies them by pairs.
For n odd, c:2n(n) = (n^n - 1*n)/(2*n)
For n even, c:2n(n) = (n^n - 2^(n-1)*n)/(2*n)

Crossrefs

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. 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
    a[0] = 1; a[n_?OddQ] := 1 + (n^n - n)/(2n); a[n_?EvenQ] := 2^(n-1) + (n^n - 2^(n-1)*n)/(2n); Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Oct 07 2017, translated from PARI *)
  • PARI
    a(n) = if(n%2, 1 + (n^n - 1*n)/(2*n), 2^(n-1) + (n^n - 2^(n-1)*n)/(2*n)); \\ Andrew Howroyd, Sep 30 2017

Formula

a(n) = 1 + (n^n - 1*n)/(2*n) if n is odd,
a(n) = 2^(n-1) + (n^n - 2^(n-1)*n)/(2*n) if n is even.

A275553 Number of classes of endofunctions of [n] under vertical translation mod n, complement to n+1 and reversal.

Original entry on oeis.org

1, 1, 2, 4, 24, 169, 2024, 29584, 525600, 10764961, 250030128, 6484436676, 185752964096, 5824523694025, 198428723433728, 7298231591777344, 288230377359679488, 12165297972404595841, 546477889989773968640, 26031837574639154232100, 1310720000002816000131072
Offset: 0

Views

Author

Olivier Gérard, Aug 05 2016

Keywords

Comments

There are three size of classes : n, 2n, 4n.
n c:n c:2n c:4n
----------------------------------
0 1
1 1
2 2
3 1 2 1
4 4 10 10
5 1 24 144
6 8 148 1868
7 1 342 29241
For n odd, only the set of n constant functions can have a member of their class equal to their complement, so c:n size is 1.
For n even, we have 2^(n/2) binary words which have mirror-symmetry
There are three types of classes of size of 2n (stable by reversal, stable by complement, stable by rc as in A275550).

Crossrefs

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. 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

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

Extensions

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

A275554 Number of classes of endofunctions of [n] under vertical translation mod n, rotation and complement to n+1.

Original entry on oeis.org

1, 1, 2, 3, 14, 65, 680, 8407, 131416, 2391515, 50006040, 1178973851, 30958827996, 896080197025, 28346960490560, 973097534189967, 36028797169965112, 1431211525754907905, 60719765554419645244, 2740193428892401092979, 131072000000281600209176
Offset: 0

Views

Author

Olivier Gérard, Aug 02 2016

Keywords

Comments

Because of the interaction between the two symmetries indexed by n, classes can be of size from n up to 2*n^2.
.
n possible class sizes
-------------------------------
1 1
2 2
3 3, 6, 18
4 4, 8, 16, 32
5 5, 10, 50
6 6, 12, 18, 24, 36, 72
7 7, 14, 98
.
but classes of size 2*n^2 account for the bulk of a(n).
n number of classes
-----------------------------------
1 1
2 2
3 1, 1, 1
4 2, 3, 4, 5
5 1, 2, 62
6 2, 4, 2, 2, 48, 622
7 1, 3, 8403

Crossrefs

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. 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

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

Extensions

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

A275555 Number of classes of endofunctions of [n] under vertical translation mod n, rotation and reversal.

Original entry on oeis.org

1, 1, 2, 4, 16, 77, 730, 8578, 132422, 2394795, 50031012, 1179054376, 30959574248, 896082610429, 28346986843640, 973097619619654, 36028798243701780, 1431211529242786625, 60719765604009463866, 2740193429053744941868, 131072000002841600036024
Offset: 0

Views

Author

Olivier Gérard, Aug 05 2016

Keywords

Comments

Because of the interaction between the two symmetries indexed by n, classes can be of size from n up to 2*n^2.
n possible class sizes
-----------------------------------
1 1
2 2
3 3, 6, 9
4 4, 8, 16, 32
5 5, 10, 25, 50
6 6, 12, 18, 24, 36, 72
7 7, 14, 49, 98
but classes of size 2*n^2 account for the bulk of a(n).
n number of classes
-----------------------------------
1 1
2 2
3 1, 1, 2
4 2, 3, 8, 3
5 1, 2, 24, 50
6 2, 4, 10, 2, 136, 576
7 1, 3, 342, 8232

Crossrefs

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. A275556 Classes under translation, rotation, complement and reversal
Cf. A275557 Classes under rotation and complement
Cf. A275558 Classes under rotation, complement and reversal

Programs

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

Extensions

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

A275556 Number of classes of endofunctions of [n] under vertical translation mod n, rotation, complement to n+1 and reversal.

Original entry on oeis.org

1, 1, 2, 3, 13, 45, 412, 4375, 66988, 1199038, 25033020, 589567451, 15480284910, 448042511917, 14173510363424, 486548852524671, 18014399792942108, 715605766365332673, 30359882832309625502, 1370096714607544395379, 65536000002956800104588
Offset: 0

Views

Author

Olivier Gérard, Aug 05 2016

Keywords

Comments

Because of the interaction between the two symmetries indexed by n and the two involutions, classes can be of size from n up to 4*n^2.
.
n possible class sizes
------------------------------------
1 1
2 2
3 3, 6, 18
4 4, 8, 16, 32, 64
5 5, 10, 50, 100
6 6, 12, 18, 24, 36, 72, 144
7 7, 14, 98, 196
.
but classes of size 4*n^2 account for the bulk of a(n).
n number of classes
------------------------------------
1 1
2 2
3 1, 1, 1
4 2, 3, 4, 3, 1
5 1, 2, 22, 20
6 2, 4, 2, 2, 28, 116, 258
7 1, 3, 339, 4032

Crossrefs

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. A275557 Classes under rotation and complement
Cf. A275558 Classes under rotation, complement and reversal

Programs

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

Extensions

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