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Search: id:A124878
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| 5, 13, 223, 4861, 197698279, 25472027467, 6975593267347, 218572480850557, 1592457339642613, 2955634782407818711841368777079578319, 2950127241932882597818337002939124083061
(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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FORMULA
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a(n) = A027612[ A124879(n) ].
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EXAMPLE
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A027612(n) begins {1, 5, 13, 77, 87, 223, 481, 4609, 4861, ...}.
Thus a(1) = 5, a(2) = 13, a(3) = 223, a(4) = 4861.
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MATHEMATICA
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s=1; Do[s=s+1/(n+1); f=Numerator[(n+1)*(s-1)]; If[PrimeQ[f], Print[{n, f}]], {n, 1, 1942}]
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CROSSREFS
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A027612(n) are the numerators of second order harmonic numbers H(n, (2)) = Sum[HarmonicNumber[k], {k, 1, n}]. Corresponding numbers n such that A027612(n) is prime are listed in A124879(n) = {2, 3, 6, 9, 18, 25, 29, 30, 39, 84, 91, 125, 130, 184, 195, 199, ...}.
Cf. A001008, A002805, A067657, A056903, A027612, A124879, A124837, A124880, A124881.
Sequence in context: A159261 A117077 A124924 this_sequence A085554 A067135 A122900
Adjacent sequences: A124875 A124876 A124877 this_sequence A124879 A124880 A124881
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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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