OFFSET
1,1
COMMENTS
Two together with primes p such that p and p+4 are both primes.
EXAMPLE
a(1)=2 because 2+5/2-3/2=3(prime) and 2+5/2+3/2=6(nonprime); a(2)=3 because 3+5/2-3/2=4(nonprime) and 3+5/2+3/2=7(prime).
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Jan 29 2010
EXTENSIONS
Entries checked by R. J. Mathar, May 02 2010
STATUS
approved