|
|
A124881
|
|
Numbers k such that A124837(k) is prime.
|
|
3
|
|
|
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
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
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)).
|
|
KEYWORD
|
hard,nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|