The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 (list; graph; refs; listen; history; text; internal format)
 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 V. Raman, Table of n, a(n) for n = 1..83 Samuel S. Wagstaff, Jr. The Cunningham Project CROSSREFS Sequence in context: A020617 A299760 A020589 * A230227 A101635 A118941 Adjacent sequences:  A216520 A216521 A216522 * A216524 A216525 A216526 KEYWORD nonn AUTHOR V. Raman, Sep 08 2012 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 4 18:15 EDT 2021. Contains 346455 sequences. (Running on oeis4.)