A124881 - OEIS

%I #12 Jan 30 2021 01:57:39

%S 2,3,9,15,25,27,33,45,55,67,70,93,94,97,112,113,125,137,189,193,212,

%T 232,262,273,281,381,453,528,670,677,742,743,827,996,1257,1349,1402,

%U 1645,1683,2110,2217,2408,2480,2623,3208,3517,3637,3665,4571,4730

%N Numbers k such that A124837(k) is prime.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/HarmonicNumber.html">Harmonic Number</a>.

%e A124837(n) begins {1, 7, 47, 57, 459, 341, 3349, 3601, 42131, 44441, ...}.

%e Thus a(1) = 2, a(2) = 3, a(3) = 9.

%t 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}]

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

%Y Corresponding primes in A124837 are listed in A124880.

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

%K hard,nonn

%O 1,1

%A _Alexander Adamchuk_, Nov 11 2006

%E More terms from _Stefan Steinerberger_, May 09 2007

%E Crossrefs edited by _Michel Marcus_, Jul 14 2018