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

1,16

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000

Formula

a(1) = 1; a(n) = Sum_{d|n, n/d > 3} a(d).

Example

a(20) = 3: 20 = 4*5 = 5*4.

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}]

Prog

(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

Crossrefs

Cf. A002033, A008484, A017898, A074206, A371209, A371212, A371213.

Sequence in context: A115561 A115622 A294892 * A108886 A140886 A001492

Adjacent sequences: A371208 A371209 A371210 * A371212 A371213 A371214

Keyword

nonn

Author

Ilya Gutkovskiy, Mar 15 2024

Extensions

More terms from Antti Karttunen, Jan 15 2025

Status

approved