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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
OFFSET
1,1
COMMENTS
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.
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: A288632 A189557 A045444 * A080829 A224789 A078884
KEYWORD
easy,nonn
AUTHOR
Cino Hilliard, May 17 2007
STATUS
approved