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Search: id:A125745
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| A125745 |
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Numbers n such that the numerator of sum_{j=1..n} n^2/(2*j*(j+n))) is prime. |
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1
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| 2, 3, 4, 5, 6, 7, 12, 35, 43, 73, 77, 93, 98, 151, 166, 224, 255, 372, 596, 602, 813, 934, 1139, 1373, 1397, 1411, 1530, 1892, 1954
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Posted in response to a question from Dirk Boland.
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EXAMPLE
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a[7]=12 because sum(j=1,k,k^2/(2*j*(j+k))) = 13013256143/892371480, for k=12, 13013256143 is prime and this is the 7th such sum with a prime numerator.
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PROGRAM
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(PARI) {ls=[]; for(k=1, 250, if(ispseudoprime(numerator(sum(j=1, k, k^2/(2*j*(j+k))))), ls=concat(ls, k))); print(ls)}
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CROSSREFS
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Sequence in context: A039952 A129978 A033079 this_sequence A032990 A060810 A066336
Adjacent sequences: A125742 A125743 A125744 this_sequence A125746 A125747 A125748
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KEYWORD
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hard,nonn
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AUTHOR
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David Broadhurst (D.Broadhurst(AT)open.ac.uk), Dec 05 2006
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