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Search: id:A129782
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| A129782 |
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The upper twin prime whose lower member has a prime index. |
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+0
1
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| 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; listen)
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OFFSET
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1,1
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COMMENT
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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.
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FORMULA
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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.
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EXAMPLE
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13 is the is an 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.
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PROGRAM
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(PARI) g(n) = for(x=1, n, p1=prime(x); p2=prime(x+1); if(p1+2==p2&&isprime(x), print1 (p2", ")))
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CROSSREFS
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Sequence in context: A063910 A117249 A045444 this_sequence A080829 A078884 A154872
Adjacent sequences: A129779 A129780 A129781 this_sequence A129783 A129784 A129785
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KEYWORD
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easy,nonn
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AUTHOR
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Cino Hilliard (hillcino368(AT)hotmail.com), May 17 2007
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