OFFSET
1,2
COMMENTS
Only a(11) = 259 is a composite number for n <= 25.
Initial corresponding primes are 17, 6870733, 9723349723 and 190977764951.
EXAMPLE
a(1) = 1 because 2^4 + 1 = 17 is prime.
MATHEMATICA
Select[Range@ 2000, PrimeQ[Sum[Prime[k]^4, {k, #}] + 1] &] (* Michael De Vlieger, Nov 28 2015 *)
PROG
(PARI) a(n) = sum(k=1, n, prime(k)^4)+1;
for(n=0, 3000, if(ispseudoprime(a(n)) , print1(n, ", ")))
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Nov 27 2015
STATUS
approved