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A225562 a(n) = smallest k such that n is the n-th largest divisor of k. 3
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 (list; graph; refs; listen; history; text; internal format)
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: A166732 A022133 A212921 * 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

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Last modified October 16 05:56 EDT 2019. Contains 328046 sequences. (Running on oeis4.)