[go: up one dir, main page]

login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A208956
Triangular array read by rows. T(n,k) is the number of n-permutations that have at least k fixed points with n >= 1 and 1 <= k <= n.
2
1, 1, 1, 4, 1, 1, 15, 7, 1, 1, 76, 31, 11, 1, 1, 455, 191, 56, 16, 1, 1, 3186, 1331, 407, 92, 22, 1, 1, 25487, 10655, 3235, 771, 141, 29, 1, 1, 229384, 95887, 29143, 6883, 1339, 205, 37, 1, 1, 2293839, 958879, 291394, 68914, 13264, 2176, 286, 46, 1, 1
OFFSET
1,4
COMMENTS
Row sums = n!
LINKS
FORMULA
E.g.f. for column k: 1/(1-x) - D(x)*Sum_{i=0..k-1} x^i/i! where D(x) is the e.g.f. for A000166.
T(n,k) = Sum_{i=k..n} C(n,i)*A000166(n-i). - Alois P. Heinz, Apr 22 2013
EXAMPLE
Triangle begins:
1;
1, 1;
4, 1, 1;
15, 7, 1, 1;
76, 31, 11, 1, 1;
455, 191, 56, 16, 1, 1;
3186, 1331, 407, 92, 22, 1, 1;
...
MAPLE
b:= proc(n) b(n):= `if`(n<2, 1-n, (n-1)*(b(n-1)+b(n-2))) end:
T:= (n, k)-> add(binomial(n, i)*b(n-i), i=k..n):
seq(seq(T(n, k), k=1..n), n=1..12); # Alois P. Heinz, Apr 22 2013
MATHEMATICA
f[list_] := Select[list, #>0&]; Map[f, Transpose[Table[nn=10; d=Exp[-x]/(1-x); p=1/(1-x); s=Sum[x^i/i!, {i, 0, n}]; Drop[Range[0, nn]! CoefficientList[Series[p-s d, {x, 0, nn}], x], 1], {n, 0, 9}]]]//Flatten
CROSSREFS
Cf. A002467 (column 1), A155521 (column 2).
Sequence in context: A157013 A346876 A141724 * A271705 A320280 A343804
KEYWORD
nonn,tabl
AUTHOR
Geoffrey Critzer, Mar 03 2012
STATUS
approved