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Search: id:A124880
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| 7, 47, 42131, 23763863, 192066102203, 5733412167187, 34745876421709, 185813891783454008069, 171312804637561107990389, 29207630124216024960052176833, 6300447575454970515437116064749
(list; graph; listen)
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OFFSET
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1,1
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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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EXAMPLE
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A124837(n) begins {1, 7, 47, 57, 459, 341, 3349, 3601, 42131, 44441, ...}.
Thus a(1) = 7, a(2) = 47, a(3) = 42131.
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MATHEMATICA
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s=3/2; Do[s=s+1/n; f=Numerator[n*(n-1)/2*(s-3/2)]; If[PrimeQ[f], Print[{n-2, f}]], {n, 3, 125}]
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CROSSREFS
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A124837(n) are the numerators of third order harmonic numbers H(n, (3)) = Sum[ Sum[ HarmonicNumber[k], {k, 1, m}], {m, 1, n} ]. Corresponding numbers n such that A124837(n) is prime are listed in A124881(n) = {2, 3, 9, 15, 25, 27, 33, 45, 55, 67, 70, 93, 94, 97, 112, 113, 125, ...}.
Cf. A001008, A002805, A067657, A056903, A027612, A124878, A124879, A124837, A124881.
Sequence in context: A020465 A092480 A088143 this_sequence A081106 A036829 A004187
Adjacent sequences: A124877 A124878 A124879 this_sequence A124881 A124882 A124883
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KEYWORD
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nonn
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AUTHOR
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Alexander Adamchuk (alex(AT)kolmogorov.com), Nov 11 2006
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