A123710 Indices n such that 4 = A123709(n) = number of nonzero terms in row n of triangle A123706.

4, 6, 8, 9, 16, 25, 27, 32, 49, 64, 81, 121, 125, 128, 169, 243, 256, 289, 343, 361, 512, 529, 625, 729, 841, 961, 1024

Offset: 1

Author

Paul D. Hanna, Oct 09 2006

Keywords

• nonn
• more

Comments

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

Except for a(2)=6, these are proper prime powers, i.e., numbers p^k where k>1, p prime (A025475). - M. F. Hasler, Feb 12 2012

Crossrefs

Cf. A123706, A123709, A123711, A123712; A010766.

Programs

PARI

for(n=1,1e4, A123709(n)==4 & print1(n","))  \\ M. F. Hasler, Feb 12 2012

Formula

a(n) = A025475(n) for n>2 (conjectured). - M. F. Hasler, Feb 12 2012