OFFSET
1,5
COMMENTS
The product of four consecutive integers + 1 is always composite (a square), so a(4) = 0. Are there any more zeros in the sequence?
Since rather large numbers (up to 193 digits) are encountered in the computation, the Pocklington-Lehmer "P-1" primality test is used, as implemented in PARI 2.1.3.
EXAMPLE
1*2*3*4*5 + 1 = 121 = 11*11 and 2*3*4*5*6 + 1 = 721 = 7*103 are composite, but 3*4*5*6*7 + 1 = 2521 is prime, so a(5) = 3.
PROG
(PARI) m=1000; for(n=1, 85, b=0; k=1; while(b<1&&k<m, if(!isprime(prod(j=k, k+n-1, j)+1, 1), k++, b=1)); print1(if(k<m, k, 0), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 05 2003
EXTENSIONS
Edited and extended by Klaus Brockhaus and Don Reble, May 06 2003
STATUS
approved