OFFSET
1,6
EXAMPLE
a(6)=2 because 147+2 and 147+50 are primes;
a(10)=3 because 605+2, 605+224 and 605+324 are primes.
CROSSREFS
KEYWORD
nonn
AUTHOR
Gerasimov Sergey, Mar 27 2012
EXTENSIONS
Corrected by R. J. Mathar, Mar 30 2012
STATUS
approved