A289905 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

Other ways to Give

A289905

Square array T(n,k) (n>0, k>0) read by antidiagonals: if gcd(n,k)>1 then T(n,k)=-1, otherwise T(n,k) = the unique m such that A289815(m) = n and A289816(m) = k.

0, 1, 2, 3, -1, 6, 9, 5, 7, 18, 27, -1, -1, -1, 54, 4, 11, 15, 21, 19, 8, 81, -1, 33, -1, 57, -1, 162, 243, 29, -1, 45, 63, -1, 55, 486, 729, -1, 87, -1, -1, -1, 165, -1, 1458, 10, 83, 249, 99, 22, 17, 171, 489, 163, 20, 2187, -1, -1, -1, 135, -1, 189, -1, -1

(list; table; graph; refs; listen; history; text; internal format)

OFFSET

1,3

COMMENTS

This sequence, when restricted to the pairs of coprime numbers, is the inverse of the function n -> (A289815(n), A289816(n)).

If n and k are coprime, then the number of nonzero digits of the ternary representation of T(n,k) equals the number of distinct prime factors of n*k.

LINKS

Rémy Sigrist, Table of n, a(n) for n = 1..5050

Rémy Sigrist, PARI program for A289905

EXAMPLE

The table begins:

x\y: 1 2 3 4 5 6 7 8 ...