A321379 Number of ways to write n as n = a*b*c*d with 1 < a <= b <= c <= d < n.

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

Offset: 1

Author

Seiichi Manyama, Nov 08 2018

Keywords

• nonn

Comments

This sequence is different from A101638.

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

Examples

			16 = 2*2*2*2. So a(16) = 1.
24 = 2*2*2*3. So a(24) = 1.
		

Links

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

Crossrefs

Cf. A026810, A122179, A218320.

Programs

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