A112983 a(n) = 2^(n+1) mod n.

0, 0, 1, 0, 4, 2, 4, 0, 7, 8, 4, 8, 4, 8, 1, 0, 4, 2, 4, 12, 16, 8, 4, 8, 14, 8, 25, 4, 4, 8, 4, 0, 16, 8, 1, 20, 4, 8, 16, 32, 4, 2, 4, 32, 34, 8, 4, 32, 11, 48, 16, 32, 4, 2, 31, 8, 16, 8, 4, 32, 4, 8, 16, 0, 64, 62, 4, 32, 16, 18, 4, 56, 4, 8, 61, 32, 36, 50, 4

Offset: 1

Author

Paul Barry, Oct 08 2005

Keywords

• easy
• nonn

Examples

			a(3) = 2^4 mod 3 = 16 mod 3 = 1.
		

Links

• T. D. Noe, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A106262, A212844.

Programs

Magma

[Modexp(2,n+1,n): n in [1..120]]; // G. C. Greubel, Jan 11 2023

Mathematica

Table[PowerMod[2, n + 1, n], {n, 100}] (* T. D. Noe, Aug 13 2012 *)

Python

print([2**(n+1) % n for n in range(1,77)])
# Alex Ratushnyak, Aug 12 2012

SageMath

[power_mod(2,n+1,n) for n in range(1,120)] # G. C. Greubel, Jan 11 2023

Formula

a(n) = A106262(2*n-1, n-2). - G. C. Greubel, Jan 11 2023

Extensions

Name, data and offset corrected by Alex Ratushnyak, Aug 12 2012