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A273323 a(n) = greatest number k <= n^2 having exactly n divisors, or 0 if no such k exists. 1
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

Cf. A000005, A005179, A035033.

Sequence in context: A170841 A090158 A030342 * A061966 A085328 A291347

Adjacent sequences:  A273320 A273321 A273322 * A273324 A273325 A273326

KEYWORD

nonn,easy

AUTHOR

Carlos Eduardo Olivieri, May 20 2016

STATUS

approved

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Last modified July 28 00:54 EDT 2021. Contains 346316 sequences. (Running on oeis4.)