A219547 Numbers k such that 2 times the least prime factor of 2^k + 1 is not the least m > 1 that divides sigma_k(m).

8, 16, 32, 40, 48, 56, 64, 80, 88, 96, 104, 112, 128, 136, 152, 160, 176, 184, 192, 200, 208, 224, 232, 240, 248, 256, 272, 280, 296, 304, 320, 328, 336, 344, 352, 368, 376, 384, 392, 400, 416, 424, 440, 448, 464, 472, 480, 488, 496

Offset: 1

Author

Jonathan Sondow, Nov 24 2012

Keywords

• nonn

Comments

Numbers k with 2*A002586(k) unequal to A066135(k).

A066135(n) <= 2*A002586(n) for all n (see Comments in A066135). Sequence gives those k for which A066135(k) < 2*A002586(k).

The corresponding least prime factors of 2^k + 1 are A219548.

See A007691 for references, links, and additional comments.

Examples

			A066135(n) = 6,10,6,34,6,10,6 = 2*A002586(n) for n = 1,2,3,4,5,6,7, and A066135(8) = 84 < 2*257 = 2*A002586(8), so a(1) = 8.
		

Crossrefs

Cf. A002586, A007691, A066135, A219548.

Formula

A066135(a(n)) < 2*A002586(a(n)).

A002586(a(n)) = A219548(n).