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A351907
Number of prime quadruples p < q < r < prime(n) in arithmetic progression.
2
0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 2, 0, 0, 0, 0, 1, 1, 0, 2, 1, 1, 1, 0, 1, 1, 3, 0, 1, 1, 1, 2, 1, 2, 1, 0, 1, 2, 1, 2, 1, 0, 3, 3, 1, 2, 1, 1, 1, 3, 1, 1, 1, 0, 2, 4, 3, 1, 1, 1, 2, 2, 0, 2, 1, 4, 2, 2, 1, 0, 2, 4, 2, 3, 1, 2, 3, 2, 3, 2, 3, 3, 2, 1, 4, 3, 2, 2, 2, 0, 1, 4, 1, 1
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
Cf. A351908 (partial sums).
Sequence in context: A174875 A193510 A353337 * A357374 A264048 A101257
KEYWORD
nonn
AUTHOR
STATUS
approved