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

Author

Alexander Adamchuk, Nov 11 2006

Keywords

• hard
• nonn

Examples

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

Links

• Eric Weisstein's World of Mathematics, Harmonic Number.

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.

Programs

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}]

Extensions

More terms from Stefan Steinerberger, May 09 2007

Crossrefs edited by Michel Marcus, Jul 14 2018