A371209 Number of ordered factorizations of n into factors > 2.
1, 0, 1, 1, 1, 1, 1, 1, 2, 1, 1, 3, 1, 1, 3, 2, 1, 3, 1, 3, 3, 1, 1, 5, 2, 1, 4, 3, 1, 5, 1, 3, 3, 1, 3, 9, 1, 1, 3, 5, 1, 5, 1, 3, 8, 1, 1, 10, 2, 3, 3, 3, 1, 8, 3, 5, 3, 1, 1, 15, 1, 1, 8, 5, 3, 5, 1, 3, 3, 5, 1, 18, 1, 1, 8, 3, 3, 5, 1, 10, 8, 1, 1, 15, 3, 1, 3
Offset: 1
Keywords
Examples
a(12) = 3: 12 = 3*4 = 4*3.
Links
- Amiram Eldar, Table of n, a(n) for n = 1..10000
Programs
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Mathematica
a[n_] := a[n] = If[n == 1, n, Sum[If[n/d > 2, a[d], 0], {d, Divisors[n]}]]; Table[a[n], {n, 1, 87}]
Formula
a(1) = 1; a(n) = Sum_{d|n, n/d > 2} a(d).