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%I #16 Sep 08 2022 08:46:13
%S 1,2,8,85,308
%N Values of n such that prime(n)! - n! + 1 is a prime number.
%C Inspired by A261457.
%C Initial primes of the form prime(n)! - n! + 1 are 2, 5, 121645100408791681.
%e For n=1, prime(1)!-1!+1 = 2 is a prime number.
%t Select[Range[400], PrimeQ[Prime[#]! - #! + 1] &] (* _Vincenzo Librandi_, Aug 31 2015 *)
%o (PARI) for(n=1, 1e3, if(isprime(prime(n)!-n!+1), print1(n", ")))
%o (Magma) [n: n in [1..80] | IsPrime(Factorial(NthPrime(n))-Factorial(n)+1)]; // _Vincenzo Librandi_, Aug 31 2015
%Y Cf. A261457.
%K nonn,more
%O 1,2
%A _Altug Alkan_, Aug 30 2015
%E a(4)-a(5) from _Giovanni Resta_, Aug 30 2015
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