A247094 Integers of the form (2^k + 1)/(2k + 1).

1, 2, 3, 5, 27, 565, 7085, 48771, 1266205, 9099507, 17602325, 128207979, 26494256091, 11147523830125, 84179432287299, 165269711096165, 281629680514649643, 4246732448623781667, 126774939137440139965, 1925041114036033717685, 14833445639443302757131

Offset: 1

Author

Juri-Stepan Gerasimov, Nov 18 2014

Keywords

• nonn

Comments

a(A103579(n)) is a subsequence.

Numbers n such that 2n + 1 divides 2^n + 1: 0, 1, 2, 5, 6, 9, 14, 18, 21, 26, 29, 30, 33, 41, 50, 53, ...

Examples

			1 is in this sequence because (2^1 + 1)/(2*1 + 1) = 1,
2 is in this sequence because (2^0 + 1)/(2*0 + 1) = 2,
3 is in this sequence because (2^5 + 1)/(2*5 + 1) = 3.
		

Links

• Colin Barker, Table of n, a(n) for n = 1..400

Crossrefs

Cf. A081856, A081858, A103579, A224486, A247132.

Programs

PARI

s=[]; for(k=0, 100, t=(2^k + 1)/(2*k + 1); if(type(t)=="t_INT", s=concat(s, t))); s=vecsort(s,,8) \\ Colin Barker, Nov 18 2014

Extensions

a(19) corrected by Colin Barker, Nov 18 2014