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 A306995 Number of primes q < prime(n), such that 2*prime(n) + q is prime. 2

%I #12 Apr 10 2019 22:31:55

%S 0,0,1,2,1,3,3,2,2,2,3,3,3,5,6,4,3,5,7,3,6,5,6,6,7,5,5,8,6,7,8,5,9,9,

%T 4,8,8,12,8,10,8,9,11,10,10,10,8,10,12,9,10,10,11,11,9,10,11,13,15,11,

%U 12,13,14,11,16,15,11,13,10,15,14,12,13,16,16,13,17,15,15

%N Number of primes q < prime(n), such that 2*prime(n) + q is prime.

%C Conjecture: a(n) > 0 for all n >= 3. - _Dmitry Kamenetsky_, Mar 18 2019

%F a(n) = A071127(prime(n)). - _Michel Marcus_, Mar 19 2019

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

%o (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

%Y Cf. A071127, A306996, A306997.

%K nonn

%O 1,4

%A _Dmitry Kamenetsky_, Mar 18 2019

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Last modified July 15 09:15 EDT 2024. Contains 374324 sequences. (Running on oeis4.)