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A272988 Convolution of the sequence of derangement numbers A000166 with itself. 1
1, 0, 2, 4, 19, 92, 552, 3832, 30453, 272552, 2713710, 29752156, 356133959, 4620985700, 64600445812, 967927029168, 15473320537001, 262864036323600, 4728905854617562, 89808092596277364, 1795480569403712699, 37693097921348983852, 829024574048725950016, 19063166411687276701736 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Vaclav Kotesovec, Table of n, a(n) for n = 0..440

FORMULA

a(n) = Sum_{i=0..n} A000166(i)*A000166(n-i).

G.f.: ( 1/(1 + x) + Sum_{k>=1} k^k*x^k/(1 + (k + 1)*x)^(k+1) )^2. - Ilya Gutkovskiy, Apr 13 2017

a(n) ~ 2*exp(-1)*n!. - Vaclav Kotesovec, Apr 13 2017

EXAMPLE

For n = 4, we get 1*9 + 0*2 + 1*1 + 2*0 + 9*1 = 19.

MATHEMATICA

Table[Sum[Subfactorial[k] Subfactorial[n - k], {k, 0, n}], {n, 0, 30}] (* Emanuele Munarini, Oct 06 2017 *)

CROSSREFS

Cf. A000166.

Sequence in context: A064228 A226891 A289269 * A168246 A212923 A058130

Adjacent sequences:  A272985 A272986 A272987 * A272989 A272990 A272991

KEYWORD

easy,nonn

AUTHOR

J. C. George, May 12 2016

STATUS

approved

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Last modified October 21 02:41 EDT 2018. Contains 316405 sequences. (Running on oeis4.)