A175893 Numbers m such that 2*prime(m)+prime(m+1) is prime.

1, 2, 3, 6, 7, 8, 10, 17, 22, 27, 29, 30, 35, 45, 48, 49, 50, 52, 53, 57, 61, 68, 70, 80, 81, 85, 94, 104, 106, 117, 120, 125, 126, 127, 131, 132, 136, 137, 138, 143, 146, 156, 157, 166, 177, 191, 198, 206, 220, 223, 224, 225, 233, 236, 244, 248, 254, 259, 261, 262

Offset: 1

Author

Zak Seidov, Oct 10 2010

Keywords

• easy
• nonn

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000040 The prime numbers.

A173971 Primes p such that 2*p+NextPrime are prime numbers.

A000720 pi(n), the number of primes <= n.

Programs

Mathematica

Select[Range[300],PrimeQ[2Prime[#]+Prime[#+1]]&] (* Harvey P. Dale, Apr 05 2025 *)

PARI

{my(a=2);for(n=1,1000,my(b=nextprime(a+1));isprime(2*a+b)&print1(n,", ");a=b)}

Formula

a(n) = pi(A173971(n))=A000720(A173971(n)).