OFFSET
1,2
COMMENTS
EXAMPLE
a(3) = 3 because 2*3*5 - 2*3 - 1 = 23 is prime.
a(6) = 8 because 2*3*5*7*11*13*17*19 - 2*3*5*7*11*13*17 + 1 = 9189181 is prime.
MATHEMATICA
t = Differences[FoldList[Times, 1, Prime@ Range@ 1200]]; Select[Range@ 360, Or[PrimeQ[t[[# - 1]] + 1], PrimeQ[t[[# - 1]] - 1]] &] - 1 (* Michael De Vlieger, Nov 28 2015, after Alonso del Arte at A061720 *)
PROG
(PARI) a(n) = prod(k=1, n, prime(k));
for(n=0, 1e3, if(ispseudoprime(a(n)-a(n-1)-1) || ispseudoprime(a(n)-a(n-1)+1), print1(n, ", ")))
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Altug Alkan, Nov 27 2015
STATUS
approved