A284466 Number of compositions (ordered partitions) of n into odd divisors of n.

1, 1, 1, 2, 1, 2, 6, 2, 1, 20, 8, 2, 60, 2, 10, 450, 1, 2, 726, 2, 140, 3321, 14, 2, 5896, 572, 16, 26426, 264, 2, 394406, 2, 1, 226020, 20, 51886, 961584, 2, 22, 2044895, 38740, 2, 20959503, 2, 676, 478164163, 26, 2, 56849086, 31201, 652968, 184947044, 980, 2, 1273706934, 6620376, 153366, 1803937344

Offset: 0

Author

Ilya Gutkovskiy, Mar 27 2017

Keywords

• nonn

Examples

			a(10) = 8 because 10 has 4 divisors {1, 2, 5, 10} among which 2 are odd {1, 5} therefore we have [5, 5], [5, 1, 1, 1, 1, 1], [1, 5, 1, 1, 1, 1], [1, 1, 5, 1, 1, 1], [1, 1, 1, 5, 1, 1], [1, 1, 1, 1, 5, 1], [1, 1, 1, 1, 1, 5] and [1, 1, 1, 1, 1, 1, 1, 1, 1, 1].
		

Links

• Alois P. Heinz, Table of n, a(n) for n = 0..2000
• Index entries for sequences related to compositions

Crossrefs

Cf. A000045, A005408, A032021, A100346, A171565.

Programs

Maple

with(numtheory):
a:= proc(n) option remember; local b, l;
      l, b:= select(x-> is(x:: odd), divisors(n)),
      proc(m) option remember; `if`(m=0, 1,
         add(`if`(j>m, 0, b(m-j)), j=l))
      end; b(n)
    end:
seq(a(n), n=0..60);  # Alois P. Heinz, Mar 30 2017

Mathematica

Table[d = Divisors[n]; Coefficient[Series[1/(1 - Sum[Boole[Mod[d[[k]], 2] == 1] x^d[[k]], {k, Length[d]}]), {x, 0, n}], x, n], {n, 0, 57}]

Python

from sympy import divisors
from sympy.core.cache import cacheit
@cacheit
def a(n):
    l=[x for x in divisors(n) if x%2]
    @cacheit
    def b(m): return 1 if m==0 else sum(b(m - j) for j in l if j <= m)
    return b(n)
print([a(n) for n in range(61)]) # Indranil Ghosh, Aug 01 2017, after Maple code

Formula

a(n) = [x^n] 1/(1 - Sum_{d|n, d positive odd} x^d).

a(n) = 1 if n is a power of 2.

a(n) = 2 if n is an odd prime.