|
%I #17 Jul 09 2015 14:09:31
%S 341,902,1547,2652,4039,5768,7673,9720,12185,14886,17707,20984,25017,
%T 29386,33757,38438,43899,50500,58457,66778,75259,84170,94431,105016,
%U 116321,129122,142863,156610,170591,185082,200791,216632,233337,252042
%N Partial sums of the Fermat pseudoprimes to base 2, A001567.
%C The subsequence of pseudoprimes in this sequence begins 341; the next term exceeds a(10000) if it exists. - _Charles R Greathouse IV_, Aug 22 2012
%C The subsequence of primes in the sequence begins 7673, 17707, 33757, 270763, 484621.
%H Charles R Greathouse IV, <a href="/A172255/b172255.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = SUM[i=1..n] {odd composite numbers n such that 2^(n-1) == 1 mod n}.
%e a(15) = 341 + 561 + 645 + 1105 + 1387 + 1729 + 1905 + 2047 + 2465 + 2701 + 2821 + 3277 + 4033 + 4369 + 4371 = 33757 is prime.
%o (PARI) sums(v)=my(s); vector(#v,i, s+=v[i])
%o sums(select(n->Mod(2, n)^n==2 & !isprime(n), vector(10^5,n,2*n+1))) \\ _Charles R Greathouse IV_, Jul 09 2015
%Y Cf. A000040, A001567.
%K easy,nonn
%O 1,1
%A _Jonathan Vos Post_, Jan 29 2010
|
