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A123710
Indices n such that 4 = A123709(n) = number of nonzero terms in row n of triangle A123706.
3
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
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
KEYWORD
nonn,more
AUTHOR
Paul D. Hanna, Oct 09 2006
STATUS
approved