

A129782


The upper twin prime whose lower member has a prime index.


0



5, 7, 13, 19, 43, 61, 181, 193, 433, 463, 601, 619, 1033, 1789, 2029, 2083, 2383, 2551, 3301, 4093, 4219, 4423, 4519, 4789, 5023, 5443, 5653, 9001, 9043, 9463, 10459, 13219, 13711, 13759, 14593, 14869, 15643, 16063, 16453, 16903, 17191, 17293
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OFFSET

1,1


COMMENTS

Computing and storing the indices of lower or upper twin primes is useful in computing twinl(n) or the nth lower twin prime from a large file of primes.


LINKS

Table of n, a(n) for n=1..42.


FORMULA

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.


EXAMPLE

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.


PROG

(PARI) g(n) = for(x=1, n, p1=prime(x); p2=prime(x+1); if(p1+2==p2&&isprime(x), print1 (p2", ")))


CROSSREFS

Sequence in context: A063910 A189557 A045444 * A080829 A224789 A078884
Adjacent sequences: A129779 A129780 A129781 * A129783 A129784 A129785


KEYWORD

easy,nonn


AUTHOR

Cino Hilliard, May 17 2007


STATUS

approved



