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Search: id:A125504
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| A125504 |
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Smallest number k such that the numerator of alternating generalized harmonic number H'(k,n) = Sum[ (-1)^(i+1) * 1/i^n, {i,1,k} ] is a prime. |
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+0
1
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| 3, 2, 2, 3, 2, 19, 2, 146, 87, 3, 16, 3, 2, 249, 15, 87, 2, 699, 2
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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a(n) = 2 for n = {2,3,5,7,13,17,19,31,61,89,107,127,...} = A000043 Primes p such that 2^p - 1 is prime. 2^p - 1 is then called a Mersenne prime. a(n) = 3 for n = {1,4,10,12,24,27,39,...}. a(n) = 5 for n = {26,76,132,205,238,...}. a(n) = 9 for n = {100,200,...}. a(n) = 15 for n = {15,33,65,...}. a(21) = 18. a(22) = 13. a(41) = 6. a(72) = 11. a(173) = 8.
a(20) > 2100 [From Max Alekseyev (maxale(AT)gmail.com), Jul 07 2009]
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LINKS
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Eric Weisstein, Link to a section of The World of Mathematics. Harmonic Number.
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CROSSREFS
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Cf. A058313, A119682, A120296, A001008.
Cf. A000043.
Sequence in context: A127807 A122028 A049234 this_sequence A075392 A069901 A115039
Adjacent sequences: A125501 A125502 A125503 this_sequence A125505 A125506 A125507
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KEYWORD
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hard,more,nonn
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AUTHOR
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Alexander Adamchuk (alex(AT)kolmogorov.com), Dec 28 2006, Jan 31 2007
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EXTENSIONS
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More terms from Max Alekseyev (maxale(AT)gmail.com), Jul 07 2009
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