login
A123711
Indices n such that A123709(n) = 8 = number of nonzero terms in row n of triangle A123706.
6
12, 18, 20, 24, 28, 36, 40, 44, 45, 48, 50, 52, 54, 56, 63, 68, 72, 75, 76, 80, 88, 92, 96, 98, 99, 100, 104, 108, 112, 116, 117, 124, 135, 136, 144, 147, 148, 152, 153, 160, 162, 164, 171, 172, 175, 176, 184, 188, 189, 192, 196, 200, 207, 208, 212, 216, 224, 225
OFFSET
1,1
COMMENTS
Triangle A123706 is the matrix inverse of triangle A010766, where A010766(n,k) = [n/k].
It appears that this equals A200511, numbers of the form p^k q^m with k,m >= 1, k+m > 2 and p, q prime. - M. F. Hasler, Feb 12 2012
LINKS
MATHEMATICA
Moebius[i_, j_] := If[Divisible[i, j], MoebiusMu[i/j], 0]; A123709[n_] :=
Length[Select[Table[Moebius[n, j] - Moebius[n, j + 1], {j, 1, n}], # != 0 &]]; Select[Range[500], A123709[#] == 8 &] (* G. C. Greubel, Apr 22 2017 *)
PROG
(PARI)
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Oct 09 2006
STATUS
approved