A216521 Numbers n such that 2^n+1 can be written in the form a^2+7*b^2.

3, 15, 21, 33, 39, 57, 105, 129, 147, 159, 183, 231, 237, 273, 303, 399, 501, 633, 735, 903, 1029, 1041, 1083, 1113

Offset

1,1

Comments

These numbers of the form 2^n+1 have no prime factors congruent to 3 (mod 7) or 5 (mod 7) or 6 (mod 7) to an odd power. Also the power of 2 is not 1.

Links

Table of n, a(n) for n=1..24.

Samuel S. Wagstaff, Jr. The Cunningham Project

Crossrefs

Sequence in context: A354675 A243128 A306771 * A110172 A261274 A014493

Adjacent sequences: A216518 A216519 A216520 * A216522 A216523 A216524

Keyword

nonn

Author

V. Raman, Sep 08 2012

Status

approved