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 A233011 #6 Dec 04 2013 18:07:00 %S A233011 19,683,478483199,20921164185599 %N A233011 Primes of the form (2*n)! - n!^2 - 1. %C A233011 The 5th term a(5) has 268 digits and is too long to display in data section. %C A233011 The 7th term a(7) in the sequence has 823 digits. %C A233011 a(8) has 2030 digits; a(9) has 2264 digits (these are not included in b-file). %H A233011 K. D. Bajpai, <a href="/A233011/b233011.txt">Table of n, a(n) for n = 1..7</a> %e A233011 a(1)= 19: n= 2: (2*n)!- n!^2-1= 19 which is prime. %e A233011 a(2)= 683: n= 3: (2*n)!- n!^2-1= 683 which is prime. %p A233011 KD := proc() local a; a:=(2*n)!-n!^2-1; if isprime(a) then RETURN (a); fi; end: seq(KD(), n=1..200); %Y A233011 Cf. A055490 (primes: n! -1). %Y A233011 Cf. A118812 (primes: (2*n)!-n!+1). %K A233011 nonn %O A233011 1,1 %A A233011 _K. D. Bajpai_, Dec 03 2013