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%I #2 Mar 30 2012 17:26:35
%S 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,
%T 85,94,104,106,117,120,125,126,127,131,132,136,137,138,143,146,156,
%U 157,166,177,191,198,206,220,223,224,225,233,236,244,248,254,259,261,262
%N a(n) = m such that 2*prime(m)+prime(m+1) is prime.
%F a(n) = pi(A173971(n))=A000720(A173971(n)).
%o (PARI) {a=2;for(n=1,1000,b=nextprime(a+1);isprime(2*a+b)&print1(n,", ");a=b)
%Y Cf. A000040 The prime numbers.
%Y A173971 Primes p such that 2*p+NextPrime are prime numbers.
%Y A000720 pi(n), the number of primes <= n.
%K easy,nonn
%O 1,2
%A _Zak Seidov_, Oct 10 2010
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