A121566 a(n) is the denominator of Sum_{i=1..n} i!/(i^2).

1, 1, 2, 6, 3, 15, 15, 105, 105, 105, 105, 1155, 1155, 15015, 15015, 15015, 15015, 255255, 255255, 4849845, 4849845, 4849845, 4849845, 111546435, 111546435, 111546435, 111546435, 111546435, 111546435, 3234846615, 3234846615, 100280245065, 100280245065

Offset

0,3

Links

Table of n, a(n) for n=0..32.

Formula

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

Example

n=0: the empty sum is 0 by convention, so a(0)=1.
n=1: the sum is 1, so a(1)=1.
n=2: the sum is 1 + 1/2 = 3/2 so a(2) = 2.

Mathematica

Join[{1}, Accumulate[Table[n!/n^2, {n, 40}]]//Denominator] (* Harvey P. Dale, May 11 2019 *)

Prog

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

Crossrefs

Cf. A121565 (numerator).

Sequence in context: A330252 A368823 A372000 * A056839 A302033 A337643

Adjacent sequences: A121563 A121564 A121565 * A121567 A121568 A121569

Keyword

easy,frac,nonn

Author

Jonathan Vos Post, Aug 07 2006

Status

approved