A123712 Indices n such that 16 = A123709(n) = number of nonzero terms in row n of triangle A123706.

60, 84, 90, 120, 126, 132, 140, 150, 156, 168, 180, 198, 204, 220, 228, 234, 240, 252, 260, 264, 270, 276, 280, 294, 300, 306, 308, 312, 315, 336, 340, 342, 348, 350, 360, 364, 372, 378, 380, 396, 408, 414, 440, 444, 450, 456, 460, 468, 476, 480, 490, 492

Offset: 1

Author

Paul D. Hanna, Oct 09 2006

Keywords

• nonn

Comments

Triangle A123706 is the matrix inverse of triangle A010766, where A010766(n,k) = [n/k].

a(n) = A178212(n) for n <= 52, possibly more. [Reinhard Zumkeller, May 24 2010]

a(n) = A178212(n) for n <= 2000. - Bill McEachen, Jul 14 2024

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1200

Crossrefs

Cf. A123706, A123709, A123710, A123711, A010766.

Programs

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[6500], A123709[#] == 16 &] (* G. C. Greubel, Apr 22 2017 *)

PARI

is(n)=my(M=matrix(n, n, r, c,r\c)^-1); sum(k=1, n, M[n, k]!=0)==16 \\ Charles R Greathouse IV, Feb 09 2012