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A216521
Numbers n such that 2^n+1 can be written in the form a^2+7*b^2.
0
3, 15, 21, 33, 39, 57, 105, 129, 147, 159, 183, 231, 237, 273, 303, 399, 501, 633, 735, 903, 1029, 1041, 1083, 1113
OFFSET
1,1
COMMENTS
These 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.
CROSSREFS
Sequence in context: A354675 A243128 A306771 * A110172 A261274 A014493
KEYWORD
nonn
AUTHOR
V. Raman, Sep 08 2012
STATUS
approved