OFFSET

1,2

EXAMPLE

a(1)=1 because 6*1-1=5, 6*1+1=7, and 6*1+5=11 are all prime.

CROSSREFS

KEYWORD

nonn,easy

AUTHOR

Juri-Stepan Gerasimov, Mar 17 2010

EXTENSIONS

Corrected by Charles R Greathouse IV, Mar 18 2010

STATUS

approved