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A216517 Even numbers n such that 2^n-1 can be written in the form a^2+7*b^2. 0
6, 42, 294, 2058 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

These Mersenne 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..4.

Samuel S. Wagstaff, Jr. The Cunningham Project

CROSSREFS

Sequence in context: A057089 A110711 A156361 * A055272 A155196 A147838

Adjacent sequences:  A216514 A216515 A216516 * A216518 A216519 A216520

KEYWORD

nonn

AUTHOR

V. Raman, Sep 08 2012

STATUS

approved

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Last modified January 16 23:44 EST 2019. Contains 319206 sequences. (Running on oeis4.)