This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A231755 #14 Nov 13 2013 17:32:03 %S A231755 331,1398079,89478457,393530540239137101071, %T A231755 1730765619511609209510165443073253, %U A231755 8173309551284740577911184144801648979299941984979211421,2142584059011987034055949456454883470029603991710390447068299 %N A231755 Primes of the form (2^n-1)/3 - n. %C A231755 a(14) has 671 digits. a(15) has 2820 digits (not included in b-file). %C A231755 Alternately, primes of the form Jacobsthal(n) - n, where Jacobsthal(n) is the n-th Jacobsthal number. %H A231755 K. D. Bajpai, <a href="/A231755/b231755.txt">Table of n, a(n) for n = 1..14</a> %e A231755 a(2)= 1398079: n=22: ((2^n-(-1)^n)/3-n)= 1398079, which is prime. %e A231755 a(4)= 393530540239137101071: n=70: ((2^n-(-1)^n)/3-n)= 393530540239137101071, which is prime. %p A231755 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 A231755 (PARI) for(n=8,500,if(ispseudoprime(t=2^n\/3-n),print1(t", "))) \\ _Charles R Greathouse IV_, Nov 13 2013 %Y A231755 Cf. A001045 (Jacobsthal numbers). %Y A231755 Cf. A107036 (indices of prime Jacobsthal numbers). %Y A231755 Cf. A128209 (Jacobsthal numbers+1). %K A231755 nonn,less %O A231755 1,1 %A A231755 _K. D. Bajpai_, Nov 13 2013 %E A231755 Definition corrected by _Charles R Greathouse IV_, Nov 13 2013