|
%I #5 Oct 01 2013 21:35:22
%S 5,7,13,19,43,61,181,193,433,463,601,619,1033,1789,2029,2083,2383,
%T 2551,3301,4093,4219,4423,4519,4789,5023,5443,5653,9001,9043,9463,
%U 10459,13219,13711,13759,14593,14869,15643,16063,16453,16903,17191,17293
%N The upper twin prime whose lower member has a prime index.
%C Computing and storing the indices of lower or upper twin primes is useful in computing twinl(n) or the n-th lower twin prime from a large file of primes.
%F Every prime has an index denoting the position the prime is in the sequence 1,2,3,... For example, 5 is the 3rd prime number so 5 has index 3, 3 has index 2 etc. It is when an upper twin prime's lower member has an index that is also prime that we list the upper prime.
%e 13 is the upper twin prime of the pair 11,13. The lower member 11 is the 5th prime number and the index 5 is prime so 13 is in the table.
%o (PARI) g(n) = for(x=1,n,p1=prime(x);p2=prime(x+1);if(p1+2==p2&&isprime(x),print1 (p2",")))
%K easy,nonn
%O 1,1
%A _Cino Hilliard_, May 17 2007
|
