A191485 Numbers n=k^2-k+1 such that 2^k == 1 (mod n).

1, 3, 7, 73, 601, 8191, 262657, 8640661

Offset: 1

Author

Alzhekeyev Ascar M, Jun 03 2011

Keywords

• nonn

Comments

The elements of this sequence are elements of the sequence A002061 (Central polygonal numbers).

The first composite number is 8640661 = 31 * 211 * 1321 (31 and 211 are elements of the sequence A002061).

No more terms up to 3773299855577673.

Examples

			k = 9;
n = k^2 - k + 1 = 81 - 9 + 1 = 73;
2^9 == 1 (mod 73).
		

Programs

PARI

for(k=1,10^9,n=k^2-k+1;if( lift(Mod(2,n)^k)==1,print1(n,", "))); /* Joerg Arndt, Jun 03 2011 */