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 A143428 a(n)=least prime == -1 mod 6 such that q(n)*(q(n)+a(n))-1 and q(n)*(q(n)+a(n))+1 are twin primes with q(i)=i-th prime == 1 mod 6. 4

%I #5 Mar 31 2012 13:22:05

%S 53,11,11,11,17,53,197,227,11,53,17,53,23,17,179,269,47,311,17,11,59,

%T 41,11,53,137,11,83,53,59,17,47,17,11,47,173,269,23,101,11,137,443,53,

%U 107,263,11,23,251,17,137,383,479,353,107,173,71,197,17,107,101,179,89,17

%N a(n)=least prime == -1 mod 6 such that q(n)*(q(n)+a(n))-1 and q(n)*(q(n)+a(n))+1 are twin primes with q(i)=i-th prime == 1 mod 6.

%H Pierre CAMI, <a href="/A143428/b143428.txt">Table of n, a(n) for n = 1..10000</a>

%e q(1)=7, 7*(7+5)-1=83 prime but 85 composite

%e 7*(7+11)-1=125 composite

%e 7*(7+17)-1=167 prime but 169 composite

%e 7*(7+23)-1=209 composite

%e 7*(7+29)-1=251 prime but 253 composite

%e 7*(7+41)-1=335 composite

%e 7*(7+47)-1=377 composite

%e 7*(7+53)-1=419 419 and 421 twin primes so a(1)=53

%Y Cf. A143427, A143429, A143430.

%K nonn

%O 1,1

%A _Pierre CAMI_, Aug 14 2008

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Last modified December 9 18:33 EST 2023. Contains 367693 sequences. (Running on oeis4.)