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

1,1

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

Links

Table of n, a(n) for n=1..27.

Formula

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

Prog

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

Crossrefs

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

Sequence in context: A163282 A095404 A073540 * A075243 A024370 A367176

Adjacent sequences: A123707 A123708 A123709 * A123711 A123712 A123713

Keyword

nonn,more

Author

Paul D. Hanna, Oct 09 2006

Status

approved