A371212 - OEIS

%I #10 Jan 16 2025 17:17:23

%S 1,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,3,1,1,1,1,

%T 3,2,1,1,1,3,1,3,1,1,3,1,1,3,2,3,1,1,1,3,3,3,1,1,1,5,1,1,3,2,3,3,1,1,

%U 1,5,1,5,1,1,3,1,3,3,1,5,2,1,1,5,3,1,1,3,1,7,3,1,1,1,3,5,1,3,3,4,1,3,1,3,5,1,1,5

%N Number of ordered factorizations of n into factors > 4.

%H Antti Karttunen, <a href="/A371212/b371212.txt">Table of n, a(n) for n = 1..20000</a>

%F a(1) = 1; a(n) = Sum_{d|n, n/d > 4} a(d).

%e a(30) = 3: 30 = 5*6 = 6*5.

%t a[n_] := a[n] = If[n == 1, n, Sum[If[n/d > 4, a[d], 0], {d, Divisors[n]}]]; Table[a[n], {n, 1, 92}]

%o (PARI)

%o memoA371212 = Map();

%o A371212(n) = if(1==n,1,my(v); if(mapisdefined(memoA371212,n,&v), v, v = sumdiv(n,d,if((n/d)<=4, 0, A371212(d))); mapput(memoA371212,n,v); (v))); \\ _Antti Karttunen_, Jan 16 2025

%Y Cf. A002033, A017899, A074206, A185325, A371209, A371211, A371213.

%K nonn

%O 1,25

%A _Ilya Gutkovskiy_, Mar 15 2024

%E More terms from _Antti Karttunen_, Jan 16 2025