A238087 A129779(n+2)/A006954(n).

-1, 1, -1, 1, -5, 63, -315, 99, -675675, 135135, -1640925, 83329155, -4583103525, 5791834125, -71152682225625, 14230536445125, -26797763435625, 24833960277501375, -73881031825566590625, 8546099690638125, -106610328924292590271875

Offset: 0

Author

Paul Curtz, Feb 24 2014

Keywords

• sign

Comments

In A129779 or A097801 there is no mention of a link with the Bernoulli numbers.

It appears that a(n+6) is divisible by 4*(n+4)^2-1 and that the sum of the digits of a(n+5) is a multiple of 9.

Examples

			a(0) = -1/1, a(1) = 2/2, a(2) = -6/6, a(3) = 30/30, a(4) = -210/42 =-5.
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..200

Crossrefs

Cf. A000466.

Programs

Mathematica

a[0] = -1; a[1] = 1; a[n_] := (-1)^(n+1)*(2*n)!/(2^(n-1)*n!*Denominator[BernoulliB[2*n-2]]); Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Feb 24 2014 *)

Formula

a(n+2) = -A004193(n+1)/A000367(n+1).

Extensions

More terms from Jean-François Alcover, Feb 24 2014