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A216515 Prime numbers n such that 2^n-1 can be written in the form a^2+7*b^2. 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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 25 21:15 EDT 2021. Contains 348256 sequences. (Running on oeis4.)