A089512 Denominators used in the computation of the column sequences of array A078739 ((2,2)-Stirling2).

1, 2, 1, 18, 6, 360, 90, 12600, 2520, 680400, 113400, 52390800, 7484400, 5448643200, 681080400, 735566832000, 81729648000, 125046361440000, 12504636144000, 26134689540960000, 2375880867360000, 6585941764321920000

Offset: 2

Author

Wolfdieter Lang, Dec 01 2003

Keywords

• nonn
• easy

Comments

See A089511 for the column sequence computation of A078739.

Formula

a(n) = lcm(seq(denominator(b(n, m)), m=1..n-1)), n>=2, where b(n, m) is defined like A089511(n, m) but without the factor D(n) and lcm stands for the least common multiple of a set of numbers.

a(n) = (sqrt(2)*n!/(8*2^(n/2)))*((n^2+4n+2*sqrt(2)+3)-(n^2+4n-2*sqrt(2)+3)*(-1)^n) [offset 0]. - Paul Barry, Sep 04 2007