A101609 - OEIS

A101609

a(n) = n! * Sum_{k=1..floor(n/2)} 1/k.

0, 2, 6, 36, 180, 1320, 9240, 84000, 756000, 8285760, 91143360, 1173553920, 15256200960, 226040855040, 3390612825600, 56865153945600, 966707617075200, 18112111963545600, 344130127307366400, 7125892746964992000

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OFFSET

1,2

LINKS

Table of n, a(n) for n=1..20.

FORMULA

a(1) = 0, a(n) = a(n-1)*n + (1 + (-1)^n)*(n-1)!. - Daniel Suteu, Feb 06 2017

MATHEMATICA

Table[ n! HarmonicNumber[ Floor[ n/2]], {n, 20}] (* Robert G. Wilson v, Dec 11 2004 *)

CROSSREFS

Cf. A101610, A101611, A101612, A101613, A000254, A046673, A052517.

Sequence in context: A236692 A323945 A369080 * A281024 A152668 A213918

Adjacent sequences: A101606 A101607 A101608 * A101610 A101611 A101612

KEYWORD

nonn,easy

AUTHOR

Ralf Stephan, Dec 10 2004

STATUS

approved