A216515 Prime numbers n such that 2^n-1 can be written in the form a^2+7*b^2.

3, 7, 13, 19, 31, 61, 67, 97, 103, 109, 127, 199, 229, 241, 271, 349, 457, 499, 523, 601, 607, 673, 733, 751, 823, 877, 907, 997

Offset

1,1

Comments

These Mersenne numbers have no prime factors congruent to 3, 5 or 6 (mod 7) raised to an odd power. Also the power of 2 is not 1.

Links

Table of n, a(n) for n=1..28.

Samuel S. Wagstaff, Jr. The Cunningham Project

Crossrefs

Sequence in context: A155703 A023217 A106077 * A048977 A216518 A342822

Adjacent sequences: A216512 A216513 A216514 * A216516 A216517 A216518

Keyword

nonn

Author

V. Raman, Sep 08 2012

Status

approved