A317545 Number of multimin factorizations of n.

1, 1, 1, 2, 1, 2, 1, 4, 2, 2, 1, 5, 1, 2, 2, 8, 1, 4, 1, 5, 2, 2, 1, 12, 2, 2, 4, 5, 1, 5, 1, 16, 2, 2, 2, 11, 1, 2, 2, 12, 1, 5, 1, 5, 5, 2, 1, 28, 2, 4, 2, 5, 1, 8, 2, 12, 2, 2, 1, 15, 1, 2, 5, 32, 2, 5, 1, 5, 2, 5, 1, 29, 1, 2, 4, 5, 2, 5, 1, 28, 8, 2, 1, 15, 2, 2, 2, 12, 1, 12, 2, 5, 2, 2, 2, 64, 1, 4, 5, 11, 1, 5, 1, 12, 5

Offset: 1

Author

Gus Wiseman, Jul 31 2018

Keywords

• nonn

Comments

A multimin factorizations of n is an ordered factorization of n into factors greater than 1 such that the sequence of minimal primes dividing each factor is weakly increasing.

Examples

			The a(36) = 11 multimin factorizations:
  (36),
  (2*18), (4*9), (6*6), (12*3), (18*2),
  (2*2*9), (2*6*3), (4*3*3), (6*2*3),
  (2*2*3*3).
		

Links

• Antti Karttunen, Table of n, a(n) for n = 1..65537

Crossrefs

Cf. A007716, A020639, A034691, A255397, A296560, A300335, A317546.

Programs

Mathematica

a[n_]:=If[n==1,1,Sum[a[d],{d,Divisors[n/FactorInteger[n][[1,1]]]}]];
Array[a,100]

PARI

A317545(n) = if(1==n,1,my(spf = factor(n)[1,1]); sumdiv(n/spf,d,A317545(d))); \\ Antti Karttunen, Sep 10 2018

PARI

memo317545 = Map(); \\ Memoized version.
A317545(n) = if(1==n,1,if(mapisdefined(memo317545, n), mapget(memo317545, n), my(spf = factor(n)[1,1], v = sumdiv(n/spf,d,A317545(d))); mapput(memo317545, n, v); (v))); \\ Antti Karttunen, Sep 10 2018

Formula

a(1) = 1; a(n > 1) = Sum_{d|(n/p)} a(d), where p is the smallest prime dividing n.

Extensions

More terms from Antti Karttunen, Sep 10 2018