Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #4 Mar 12 2015 19:15:48
%S 3,5,3,5,3,5,3,5,11,5,3,5,3,5,5,11,5,3,11,5,3,5,11,3,5,3,5,3,17,3,5,
%T 11,11,17,5,5,3,5,5,11,11,5,3,29,11,11,3,5,3,5,11,29,5,5,5,11,5,3,11,
%U 29,17,3,5,3,29,5,11,5,3,5,29,5,5,3,5,11,3,17,11,11,11,11,5,3,5,11,3,5,3,11
%N Smallest lower twin prime tp such that p + tp + 1 is prime. p ranges over the prime numbers.
%C Conjecture: For all primes p <= n there is always a lower twin prime L less than n such that p+L+1 is prime.
%e 29 is the 9th odd prime. 29+3+1, 29+5+1 are not prime. 29+11+1 is prime, so a(9) = 11 the smallest lower twin prime satisfying the definition for prime 29.
%o (PARI) g(n) = ct=0;for(x=2,n,p1=prime(x);for(y=1,n,p2=twinl(y);z=p1+p2+1;
%o if(isprime(z),ct++;print1(p2",");break)));ct
%K nonn
%O 1,1
%A _Cino Hilliard_, Nov 21 2008