OFFSET
0,3
COMMENTS
As a corollary to Fermat's little theorem, (2^p - 2)/p is always an integer for p prime. - Alonso del Arte, May 04 2013
LINKS
Harry J. Smith, Table of n, a(n) for n = 0..100
FORMULA
a(n) = A001037(prime(n)) for n >= 1. - Hilko Koning, Sep 10 2018
a(n) = 2*A007663(n) for n > 1. - Jeppe Stig Nielsen, May 16 2021
EXAMPLE
a(3) = 6, because prime(3) = 5, and (2^5 - 2)/5 = 30/5 = 6.
a(4) = 18, because prime(4) = 7, and (2^7 - 2)/7 = 126/7 = 18.
MAPLE
A064535 := proc(n) ( 2^ithprime(n) - 2 )/ithprime(n); end;
MATHEMATICA
Table[(2^Prime[n] - 2)/Prime[n], {n, 50}] (* Alonso del Arte, Apr 28 2013 *)
PROG
(PARI) a(n) = if (n, (2^prime(n) - 2)/prime(n), 0); \\ Harry J. Smith, Sep 17 2009
(Magma) [0] cat [(2^NthPrime(n)-2)/NthPrime(n): n in [1..25]]; // Vincenzo Librandi, Sep 14 2018
CROSSREFS
For n > 1, this is the odd prime indexed subsequence of: A000799, A001037, A038063, A038067, A052823, A059966, A060477, A060480, A064355, A065482 (for n>2), A082482, A086442 (apparently), A093367, A095718 (apparently, up to offset), A098792, A106365, A107847, A220418, A220587 (apparently), A225101, A290261, A300329, A306156, A320783, A383034.
KEYWORD
nonn
AUTHOR
Shane Findley, Oct 09 2001
STATUS
approved