OFFSET
1,1
EXAMPLE
For n = 3: 2*3*1 +1 = 7, which is prime. 2*3*2 + 1 = 13, which is prime. 2*3*3 + 1 = 19, which is prime. But 2*3*4 + 1 = 25, which is composite. So a(3) = 3, because there are 3 primes in the arithmetic sequence before hitting a composite.
CROSSREFS
KEYWORD
nonn
AUTHOR
Leroy Quet, Oct 30 2008
EXTENSIONS
Extended by Ray Chandler, Nov 01 2008
STATUS
approved