A225562 a(n) = smallest k such that n is the n-th largest divisor of k.

1, 4, 15, 20, 30, 48, 84, 160, 144, 210, 462, 240, 624, 1134, 480, 864, 1836, 720, 8740, 840, 1512, 2376, 4968, 2400, 3900, 3120, 4536, 4032, 15312, 2520, 17856, 5280, 6930, 10710, 15400, 7200, 47952, 17100, 12480, 7920, 72324, 9240, 43344, 16632, 20790

Offset

1,2

Comments

The smallest row k such that n is the n-th entry in the triangle A056538 of divisors in reverse order.

Is a(n) defined for every n ? - Giovanni Resta, May 15 2013

Links

Alois P. Heinz and Zak Seidov, Table of n, a(n) for n = 1..1000 (first 200 terms from Alois P. Heinz)

Example

a(6) = 48 because the divisors of 48 are {48, 24, 16, 12, 8, 6, 4, 3, 2, 1} and 6 is the 6th divisor of 48.

Maple

with(numtheory):
a:= proc(n) local k;
      for k from n by n while tau(k)<n or
        sort([divisors(k)[]], `>`)[n]<>n do od; k
    end:
seq(a(n), n=1..50);  # Alois P. Heinz, May 29 2013

Mathematica

a[n_] := Block[{k = 1, d}, While[Length[d = Reverse@ Divisors@ k] < n || n != d[[n]], k++]; k]; Array[a, 20] (* Giovanni Resta, May 15 2013 *)

Crossrefs

Sequence in context: A022133 A212921 A359958 * A301707 A100783 A170850

Adjacent sequences: A225559 A225560 A225561 * A225563 A225564 A225565

Keyword

nonn

Author

Irina Gerasimova, May 13 2013

Extensions

a(13)-a(45) from Giovanni Resta, May 15 2013

Status

approved