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A321379 Number of ways to write n as n = a*b*c*d with 1 < a <= b <= c <= d < n. 1
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 2, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,48

COMMENTS

This sequence is different from A101638.

If p is prime, a(p^k) = A026810(k). - Robert Israel, Nov 08 2018

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

EXAMPLE

16 = 2*2*2*2. So a(16) = 1.

24 = 2*2*2*3. So a(24) = 1.

MAPLE

N:= 100: # for a(1)..a(N)

V:= Vector(N):

for a from 2 to floor(N^(1/4)) do

  for b from a to floor((N/a)^(1/3)) do

    for c from b to floor((N/a/b)^(1/2)) do

      for d from c to N/(a*b*c) do

        V[a*b*c*d]:= V[a*b*c*d]+1

od od od od:

convert(V, list); # Robert Israel, Nov 08 2018

CROSSREFS

Cf. A026810, A122179, A218320.

Sequence in context: A194024 A082786 A101638 * A070141 A088722 A122180

Adjacent sequences:  A321376 A321377 A321378 * A321380 A321381 A321382

KEYWORD

nonn

AUTHOR

Seiichi Manyama, Nov 08 2018

STATUS

approved

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Last modified April 25 16:59 EDT 2019. Contains 322461 sequences. (Running on oeis4.)