A121206 a(n) = (2n)! mod n(2n+1).

2, 4, 6, 0, 10, 12, 0, 16, 18, 0, 22, 0, 0, 28, 30, 0, 0, 36, 0, 40, 42, 0, 46, 0, 0, 52, 0, 0, 58, 60, 0, 0, 66, 0, 70, 72, 0, 0, 78, 0, 82, 0, 0, 88, 0, 0, 0, 96, 0, 100, 102, 0, 106, 108, 0, 112, 0, 0, 0, 0, 0, 0, 126, 0, 130, 0, 0, 136, 138, 0, 0, 0, 0, 148, 150, 0, 0, 156, 0, 0, 162

Offset: 1

Author

Ben Paul Thurston, Aug 20 2006

Keywords

• nonn

Comments

If the zeros are removed and a 3 is inserted at the front, the first 3000 terms (or more) of the condensed sequence coincide with A039915. - R. J. Mathar, Mar 02 2007

Examples

			a(4) = 0 because 8*7*6*5*4*3*2*1 / 8+7+6+5+4+3+2+1 divides evenly (0 remainder).
		

Crossrefs

Cf. A005097 gives indices of nonzero terms; A047845 gives indices of zero terms.

Cf. A039915, A006093.

Programs

Mathematica

Table[Mod[(2n)!, n*(2n + 1)], {n, 85}] (* Ray Chandler, Aug 23 2006 *)

Formula

a(n) = A000142(2n) mod A000217(2n).

Extensions

Edited, corrected and extended by R. J. Mathar and Ray Chandler, Aug 23 2006