login
A216523
Odd numbers n such that (2^n+1)/3 can be written in the form a^2+7*b^2.
1
1, 5, 7, 11, 13, 17, 19, 23, 31, 35, 43, 49, 53, 61, 67, 77, 79, 85, 89, 91, 101, 119, 121, 127, 133, 139, 161, 167, 179, 187, 191, 199, 211, 215, 217, 221, 223, 227, 245, 269, 301, 313, 317, 323, 343, 347, 361, 371, 389, 395, 427, 431, 433, 457, 469, 503, 539
OFFSET
1,2
COMMENTS
These numbers of the form (2^n+1)/3 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
Samuel S. Wagstaff, Jr. The Cunningham Project
CROSSREFS
Sequence in context: A299760 A020589 A364001 * A230227 A101635 A118941
KEYWORD
nonn
AUTHOR
V. Raman, Sep 08 2012
STATUS
approved