A121565 a(n) is the numerator of Sum_{i=1..n} i!/(i^2).

0, 1, 3, 13, 11, 127, 427, 13789, 79939, 550339, 4360579, 428990369, 4270982369, 608769618797, 7287249426797, 94552718917997, 1321723383637997, 336624987690165949, 5380569124281525949, 1736468713616949633031, 31234462813230541185031, 593101017091584665985031

Offset

0,3

Links

Table of n, a(n) for n=0..21.

Formula

Numerator of Sum_{i=1..n} A000142(i)/A000290(i).

Mathematica

Join[{0}, Accumulate[Table[k!/k^2, {k, 30}]]]//Numerator (* Harvey P. Dale, Feb 21 2024 *)

Prog

(PARI) a(n) = numerator(sum(i=1, n, i!/i^2)); \\ Michel Marcus, Mar 18 2018

Crossrefs

Cf. A121566 (denominator).

Sequence in context: A273674 A360967 A214811 * A107733 A273076 A272825

Adjacent sequences: A121562 A121563 A121564 * A121566 A121567 A121568

Keyword

easy,frac,nonn

Author

Jonathan Vos Post, Aug 07 2006

Extensions

a(0) corrected by Michel Marcus, Jun 13 2022

a(11) corrected by Georg Fischer, Jan 05 2024

Status

approved