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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 (list; graph; refs; listen; history; text; internal format)
 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. 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: A288632 A189557 A045444 * A080829 A224789 A078884 Adjacent sequences: A129779 A129780 A129781 * A129783 A129784 A129785 KEYWORD easy,nonn AUTHOR Cino Hilliard, May 17 2007 STATUS approved

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Last modified September 18 07:20 EDT 2024. Contains 375996 sequences. (Running on oeis4.)