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A144360
Primes of the form 8^k + 7. Also, primes of the form 64^m + 7.
9
71, 262151, 1073741831, 302231454903657293676551, 85070591730234615865843651857942052871, 23945242826029513411849172299223580994042798784118791, 25711008708143844408671393477458601640355247900524685364822023
OFFSET
1,1
COMMENTS
k=2m, since for odd k, 8^k + 7 is divisible by 3.
Prime numbers p in A144242 such that p-1 is the fourth a-gonal and seventh b-gonal number for some a and b. Namely, a = (8^k+14)/6 and b = (8^k + 41)/21.
This sequence appears to be a subset of A144313.
The next term has 178 digits. - Harvey P. Dale, Sep 03 2015
EXAMPLE
71 - 1 = 70 is the fourth triskaidecagonal number and seventh pentagonal number.
MATHEMATICA
Select[64^Range[40]+7, PrimeQ] (* Harvey P. Dale, Sep 03 2015 *)
PROG
(Magma) [a: n in [0..80] | IsPrime(a) where a is 8^n+7]; // Vincenzo Librandi, Aug 02 2017
KEYWORD
nonn
AUTHOR
Reikku Kulon, Sep 18 2008
EXTENSIONS
Edited by Max Alekseyev, Feb 17 2011
STATUS
approved