OFFSET
1,12
COMMENTS
We define a factorization of n into factors > 1 to be co-balanced if it has exactly A001221(n) factors.
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..65537
EXAMPLE
The a(n) co-balanced factorizations for n = 12, 24, 36, 72, 120, 144, 180:
2*6 3*8 4*9 8*9 3*5*8 2*72 4*5*9
3*4 4*6 6*6 2*36 4*5*6 3*48 5*6*6
2*12 2*18 3*24 2*2*30 4*36 2*2*45
3*12 4*18 2*3*20 6*24 2*3*30
6*12 2*4*15 8*18 2*5*18
2*5*12 9*16 2*6*15
2*6*10 12*12 2*9*10
3*4*10 3*3*20
3*4*15
3*5*12
3*6*10
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
Table[Length[Select[facs[n], Length[#]==PrimeNu[n]&]], {n, 100}]
PROG
(PARI) A340596(n, m=n, om=omega(n)) = if(1==n, (0==om), sumdiv(n, d, if((d>1)&&(d<=m), A340596(n/d, d, om-1)))); \\ Antti Karttunen, Jun 10 2024
CROSSREFS
Positions of terms > 1 are A126706.
Positions of 1's are A303554.
The version for unlabeled multiset partitions is A319616.
The alt-balanced version is A340599.
The balanced version is A340653.
The cross-balanced version is A340654.
The twice-balanced version is A340655.
A001055 counts factorizations.
A045778 counts strict factorizations.
A316439 counts factorizations by product and length.
Other balance-related sequences:
- A010054 counts balanced strict partitions.
- A047993 counts balanced partitions.
- A098124 counts balanced compositions.
- A106529 lists Heinz numbers of balanced partitions.
- A340597 lists numbers with an alt-balanced factorization.
- A340598 counts balanced set partitions.
- A340600 counts unlabeled balanced multiset partitions.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 15 2021
EXTENSIONS
Data section extended up to a(120) by Antti Karttunen, Jun 10 2024
STATUS
approved