A124881 Numbers k such that A124837(k) is prime.

2, 3, 9, 15, 25, 27, 33, 45, 55, 67, 70, 93, 94, 97, 112, 113, 125, 137, 189, 193, 212, 232, 262, 273, 281, 381, 453, 528, 670, 677, 742, 743, 827, 996, 1257, 1349, 1402, 1645, 1683, 2110, 2217, 2408, 2480, 2623, 3208, 3517, 3637, 3665, 4571, 4730

Offset

1,1

Links

Table of n, a(n) for n=1..50.

Eric Weisstein's World of Mathematics, Harmonic Number.

Example

A124837(n) begins {1, 7, 47, 57, 459, 341, 3349, 3601, 42131, 44441, ...}.
Thus a(1) = 2, a(2) = 3, a(3) = 9.

Mathematica

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, 1000}]

Crossrefs

A124837 are the numerators of third-order harmonic numbers H(n, (3)).

Corresponding primes in A124837 are listed in A124880.

Cf. A001008, A002805, A067657, A056903, A027612, A124878, A124879, A124837, A124880.

Sequence in context: A092352 A061933 A251239 * A054416 A291868 A092638

Adjacent sequences: A124878 A124879 A124880 * A124882 A124883 A124884

Keyword

hard,nonn

Author

Alexander Adamchuk, Nov 11 2006

Extensions

More terms from Stefan Steinerberger, May 09 2007

Crossrefs edited by Michel Marcus, Jul 14 2018

Status

approved