A217897 - OEIS

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A217897

Triangular array read by rows. T(n,k) is the number of unlabeled functions on n nodes that have exactly k fixed points, n >= 0, 0 <= k <= n.

1, 0, 1, 1, 1, 1, 2, 3, 1, 1, 6, 7, 4, 1, 1, 13, 19, 9, 4, 1, 1, 40, 47, 27, 10, 4, 1, 1, 100, 130, 68, 29, 10, 4, 1, 1, 291, 343, 195, 76, 30, 10, 4, 1, 1, 797, 951, 523, 220, 78, 30, 10, 4, 1, 1, 2273, 2615, 1477, 600, 228, 79, 30, 10, 4, 1, 1, 6389, 7318, 4096, 1708, 625, 230, 79, 30, 10, 4, 1, 1

(list; table; graph; refs; listen; history; text; internal format)

OFFSET

0,7

COMMENTS

Row sums are A001372;

Column for k=0 is A001373;

Column for k=1 is A001372. (offset)

LINKS

Table of n, a(n) for n=0..77.

N. J. A. Sloane, Illustration of initial terms of A001372

FORMULA

O.g.f.: Product_{n>=1} 1/((1-x^n)^A002862(n) * (1 - y*x^n)^A000081(n) ).

EXAMPLE

Triangle begins:

0, 1;

1, 1, 1;

2, 3, 1, 1;

6, 7, 4, 1, 1;

13, 19, 9, 4, 1, 1;

40, 47, 27, 10, 4, 1, 1;

100, 130, 68, 29, 10, 4, 1, 1;

291, 343, 195, 76, 30, 10, 4, 1, 1;

797, 951, 523, 220, 78, 30, 10, 4, 1, 1;

2273, 2615, 1477, 600, 228, 79, 30, 10, 4, 1, 1;

MATHEMATICA

Needs["Combinatorica`"]; nn=30; s[n_, k_]:=s[n, k]=a[n+1-k]+If[n<2 k, 0, s[n-k, k]]; a[1]=1; a[n_]:=a[n]=Sum[a[i] s[n-1, i] i, {i, 1, n-1}]/(n-1); rt=Table[a[i], {i, 1, nn}]; cfd=Drop[Apply[Plus, Table[Take[CoefficientList[CycleIndex[CyclicGroup[n], s]/.Table[s[j]->Table[Sum[rt[[i]] x^(k*i), {i, 1, nn}], {k, 1, nn}][[j]], {j, 1, nn}], x], nn], {n, 2, 30}]], 1]; CoefficientList[Series[Product[1/(1-x^i)^cfd[[i]]/(1-y x^i)^rt[[i]], {i, 1, nn-1}], {x, 0, 10}], {x, y}]//Grid (* after code given by Robert A. Russell in A000081 *)

CROSSREFS

Sequence in context: A068348 A308290 A204167 * A135900 A338072 A173272

Adjacent sequences: A217894 A217895 A217896 * A217898 A217899 A217900

KEYWORD

nonn,tabl

AUTHOR

Geoffrey Critzer, Oct 14 2012

STATUS

approved