OFFSET
1,2
COMMENTS
N is in the sequence iff semiprime(n) is of the form 2p where p is a Sophie Germain prime (A005384).
EXAMPLE
a(1)=1 because semiprime(1)+1=5=prime, a(2)=2 because semiprime(2)+1=7=prime, a(3)=4 because semiprime(4)+1=11=prime.
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Mar 30 2010
EXTENSIONS
Edited, corrected and extended by Ray Chandler, Apr 05 2010
STATUS
approved