OFFSET
1,3
EXAMPLE
a(1)=0 because 2*0^2-11=-11=nonprime and 2*0^2+11=11=prime; a(2)=1 because 2*1^2-11=-9=nonprime and 2*1^2+11=13=prime; a(3)=2 because 2*2^2-11=-3=nonprime and 2*2^2+11=19=prime; a(4)=4 because 2*4^2-11=21=nonprime and 2*4^2+11=43=prime.
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Mar 09 2010
EXTENSIONS
Corrected (15 removed) and extended beyond 71 by R. J. Mathar, Apr 20 2010
STATUS
approved