A371211 Number of ordered factorizations of n into factors > 3.
1, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 3, 2, 1, 1, 3, 1, 3, 1, 3, 1, 1, 3, 4, 1, 1, 1, 5, 1, 3, 1, 3, 3, 1, 1, 5, 2, 3, 1, 3, 1, 3, 3, 5, 1, 1, 1, 7, 1, 1, 3, 5, 3, 3, 1, 3, 1, 5, 1, 7, 1, 1, 3, 3, 3, 3, 1, 10, 2, 1, 1, 7, 3, 1, 1, 5, 1, 7, 3, 3, 1, 1, 3, 10, 1, 3, 3, 9, 1, 3, 1, 5, 5
Offset: 1
Keywords
Examples
a(20) = 3: 20 = 4*5 = 5*4.
Links
- Antti Karttunen, Table of n, a(n) for n = 1..20000
Programs
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Mathematica
a[n_] := a[n] = If[n == 1, n, Sum[If[n/d > 3, a[d], 0], {d, Divisors[n]}]]; Table[a[n], {n, 1, 89}] -
PARI
memoA371211 = Map(); A371211(n) = if(1==n,1,my(v); if(mapisdefined(memoA371211,n,&v), v, v = sumdiv(n,d,if((n/d)<=3, 0, A371211(d))); mapput(memoA371211,n,v); (v))); \\ Antti Karttunen, Jan 15 2025
Formula
a(1) = 1; a(n) = Sum_{d|n, n/d > 3} a(d).
Extensions
More terms from Antti Karttunen, Jan 15 2025