OFFSET
1,1
EXAMPLE
n=144:3n=432,6n=864, a(144)=120097 prime with (120097-1)/864=139 prime and with 864.12097+1=103763809 prime.
PROG
(PARI) a(n) = {n = 3*n; p = 2; while (!(isprime(2*n*p+1) && (type(q=(p-1)/(2*n))== "t_INT") && isprime(q)), p = nextprime(p+1)); p; } \\ Michel Marcus, Feb 25 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Labos Elemer, Jul 22 2003
STATUS
approved