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A144657 a(n) = Sum[Sum[(i+j)!/(i!*j!),{i,1,n}],{j,1,n}]. 2
0, 2, 14, 62, 242, 912, 3418, 12854, 48602, 184736, 705410, 2704132, 10400574, 40116572, 155117490, 601080358, 2333606186, 9075135264, 35345263762, 137846528780, 538257874398, 2104098963676, 8233430727554 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

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

FORMULA

Recurrence: (n+1)*(12*n-19)*a(n) = 2*(30*n^2 - 24*n - 19)*a(n-1) - (48*n^2 - 9*n - 7)*a(n-2) - 2*(2*n-3)*a(n-3). - Vaclav Kotesovec, Oct 20 2012

a(n) ~ 4^(n+1)/sqrt(Pi*n). - Vaclav Kotesovec, Oct 20 2012

MATHEMATICA

Table[Sum[Sum[(i+j)!/i!/j!, {i, 1, n}], {j, 1, n}], {n, 0, 20}] (* corrected by Vaclav Kotesovec, Oct 20 2012 *)

CROSSREFS

Suggested by a formula in A048775.

Sequence in context: A153332 A331822 A217154 * A167555 A222445 A181394

Adjacent sequences:  A144654 A144655 A144656 * A144658 A144659 A144660

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Jan 30 2009

STATUS

approved

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Last modified March 28 17:51 EDT 2020. Contains 333103 sequences. (Running on oeis4.)