A290044 - OEIS

A290044

a(n) = |Sum_{k=0..n} (-1)^k*(2k)!!|.

1, 1, 7, 41, 343, 3497, 42583, 602537, 9719383, 176075177, 3539816023, 78209790377, 1883780763223, 49127973630377, 1379201149390423, 41470672541233577, 329725285558734423, 45290937289840177577, 1633052915424520654423, 62144013487721190961577

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

OFFSET

0,3

COMMENTS

a(20) = 19 * 47 * 73 * 54470291 * 700938921577. Thus a(n) are multiples of 19 for n >= 20.

LINKS

Table of n, a(n) for n=0..19.

MATHEMATICA

Table[Abs@ Sum[(-1)^k*(2 k)!!, {k, 0, n}], {n, 0, 19}] (* Michael De Vlieger, Jul 19 2017 *)

CROSSREFS

Cf. A006882, A138525.

Sequence in context: A125120 A353992 A181441 * A209113 A146991 A377347

Adjacent sequences: A290041 A290042 A290043 * A290045 A290046 A290047

KEYWORD

easy,nonn

AUTHOR

XU Pingya, Jul 19 2017

STATUS

approved