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A280654
a(n) = (n!)^2 * Sum_{k=1..n} A008836(k)/k^2.
2
1, 3, 23, 404, 9524, 357264, 16987536, 1061800704, 87631559424, 8894837836800, 1063107188812800, 151494084266803200, 25373057708287180800, 5011895098867920076800, 1135276451701834014720000, 292340783888393707192320000, 84048723407048386326036480000
OFFSET
1,2
LINKS
FORMULA
Limit_{n->infinity} a(n)/(n!)^2 = zeta(4)/zeta(2) = Pi^2/15.
MATHEMATICA
Table[(n!)^2 * Sum[(-1)^PrimeOmega[k]/k^2, {k, n}], {n, 20}] (* Indranil Ghosh, Apr 13 2017 *)
PROG
(PARI) a(n) = (n!)^2 * sum(k=1, n, (-1)^bigomega(k)/k^2);
CROSSREFS
Cf. A001044, A008836, A182448 (Pi^2/15).
Sequence in context: A114601 A178315 A210910 * A118195 A055326 A271851
KEYWORD
nonn
AUTHOR
Daniel Suteu, Apr 12 2017
STATUS
approved