A178970 a(n) = 2^(2n-1) mod (2n+1).

2, 3, 4, 2, 6, 7, 2, 9, 10, 2, 12, 8, 20, 15, 16, 2, 22, 19, 2, 21, 22, 38, 24, 32, 2, 27, 52, 2, 30, 31, 2, 8, 34, 2, 36, 37, 17, 43, 40, 20, 42, 8, 2, 45, 32, 2, 27, 49, 29, 51, 52, 23, 54, 55, 2, 57, 77, 11, 15, 28, 2, 108, 64, 2, 66, 32, 47, 69, 70, 2

Offset: 1

Author

Juri-Stepan Gerasimov, Jan 03 2011

Keywords

• nonn

Examples

			a(1) = 2^(2*1-1) mod (2*1+1) = 2^1 mod 3 = 2.
		

Crossrefs

Cf. A000079.

Programs

Mathematica

f[n_] := PowerMod[2, 2 n - 1, 2 n + 1]; Array[f, 70] (* Robert G. Wilson v, Jan 03 2011 *)

Formula

a(n) = A081294(n) mod A005408(n).