1,4

Conjecture: a(n) > 0 for all n >= 3. - Dmitry Kamenetsky, Mar 18 2019

Table of n, a(n) for n=1..79.

a(n) = A071127(prime(n)). - Michel Marcus, Mar 19 2019

2*7 + 3 = 17 and 2*7 + 5 = 19 are prime. Hence a(4) = 2.

(PARI) a(n) = my(s=0, p=prime(n)); forprime(i=1, p-1, s += isprime(2*p+i)); s; \\ Michel Marcus, Mar 19 2019

Cf. A071127, A306996, A306997.

Sequence in context: A337137 A035050 A198790 * A212907 A308584 A046819

Adjacent sequences: A306992 A306993 A306994 * A306996 A306997 A306998

nonn

Dmitry Kamenetsky, Mar 18 2019

approved