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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

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