A273323 - 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

A273323

a(n) = greatest number k <= n^2 having exactly n divisors, or 0 if no such k exists.

1, 3, 9, 15, 16, 32, 0, 56, 36, 80, 0, 140, 0, 192, 144, 216, 0, 300, 0, 336, 0, 0, 0, 540, 0, 0, 0, 0, 0, 720, 0, 840, 0, 0, 0, 1260, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0

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

OFFSET

1,2

COMMENTS

The sequence is zero for n>36, since A005179(n) > n^2 for all n > 36.

LINKS

Table of n, a(n) for n=1..78.

EXAMPLE

a(4) = 15, because 15 is the greatest number <= 4^2 with exactly 4 divisors.

MATHEMATICA

Seq := {}; For[n = 1, n < 50, n++, AppendTo[Seq, a = Max[Select[Range[n^2], DivisorSigma[0, #] == n &]]; If[a == -Infinity, 0, a]]]; Seq

CROSSREFS