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%I #14 Nov 13 2013 17:32:03
%S 331,1398079,89478457,393530540239137101071,
%T 1730765619511609209510165443073253,
%U 8173309551284740577911184144801648979299941984979211421,2142584059011987034055949456454883470029603991710390447068299
%N Primes of the form (2^n-1)/3 - n.
%C a(14) has 671 digits. a(15) has 2820 digits (not included in b-file).
%C Alternately, primes of the form Jacobsthal(n) - n, where Jacobsthal(n) is the n-th Jacobsthal number.
%H K. D. Bajpai, <a href="/A231755/b231755.txt">Table of n, a(n) for n = 1..14</a>
%e a(2)= 1398079: n=22: ((2^n-(-1)^n)/3-n)= 1398079, which is prime.
%e a(4)= 393530540239137101071: n=70: ((2^n-(-1)^n)/3-n)= 393530540239137101071, which is prime.
%p KD := proc() local a; a:= (2^n -(-1)^n)/3-n; if isprime(a)then RETURN (a); fi; end: seq(KD(),n=1..1000);
%o (PARI) for(n=8,500,if(ispseudoprime(t=2^n\/3-n),print1(t", "))) \\ _Charles R Greathouse IV_, Nov 13 2013
%Y Cf. A001045 (Jacobsthal numbers).
%Y Cf. A107036 (indices of prime Jacobsthal numbers).
%Y Cf. A128209 (Jacobsthal numbers+1).
%K nonn,less
%O 1,1
%A _K. D. Bajpai_, Nov 13 2013
%E Definition corrected by _Charles R Greathouse IV_, Nov 13 2013
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