OFFSET
1,17
EXAMPLE
a(9) = 1 corresponds to the quadruple (5, 11, 17, 23) where 23 is the 9th prime.
PROG
(PARI) a(n, q=prime(n))=my(s); forprimestep(p=q%6, q-18, 6, isprime((2*p+q)/3) && isprime((2*q+p)/3) && s++); s
CROSSREFS
KEYWORD
nonn
AUTHOR
Charles R Greathouse IV, Feb 25 2022
STATUS
approved