A233011 - OEIS

%I #6 Dec 04 2013 18:07:00

%S 19,683,478483199,20921164185599

%N Primes of the form (2*n)! - n!^2 - 1.

%C The 5th term a(5) has 268 digits and is too long to display in data section.

%C The 7th term a(7) in the sequence has 823 digits.

%C a(8) has 2030 digits; a(9) has 2264 digits (these are not included in b-file).

%H K. D. Bajpai, <a href="/A233011/b233011.txt">Table of n, a(n) for n = 1..7</a>

%e a(1)= 19: n= 2: (2*n)!- n!^2-1= 19 which is prime.

%e a(2)= 683: n= 3: (2*n)!- n!^2-1= 683 which is prime.

%p KD := proc() local a; a:=(2*n)!-n!^2-1; if isprime(a) then RETURN (a);  fi; end: seq(KD(), n=1..200);

%Y Cf. A055490 (primes: n! -1).

%Y Cf. A118812 (primes: (2*n)!-n!+1).

%K nonn

%O 1,1

%A _K. D. Bajpai_, Dec 03 2013