OFFSET
0,3
COMMENTS
The n-th superprimorial is A006939(n) = Product_{i = 1..n} prime(i)^(n - i + 1).
Also the number of strict multiset partitions of {1,2,2,3,3,3,...,n}, a multiset with i copies of i for i = 1..n.
FORMULA
EXAMPLE
The a(3) = 34 factorizations:
2*3*4*15 2*3*60 2*180 360
2*3*5*12 2*4*45 3*120
2*3*6*10 2*5*36 4*90
2*4*5*9 2*6*30 5*72
3*4*5*6 2*9*20 6*60
2*10*18 8*45
2*12*15 9*40
3*4*30 10*36
3*5*24 12*30
3*6*20 15*24
3*8*15 18*20
3*10*12
4*5*18
4*6*15
4*9*10
5*6*12
5*8*9
MATHEMATICA
chern[n_]:=Product[Prime[i]^(n-i+1), {i, n}];
stfa[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[stfa[n/d], Min@@#>d&]], {d, Rest[Divisors[n]]}]];
Table[Length[stfa[chern[n]]], {n, 0, 3}]
PROG
(PARI) \\ See A318286 for count.
a(n) = {if(n==0, 1, count(vector(n, i, i)))} \\ Andrew Howroyd, Sep 01 2020
CROSSREFS
A022915 counts permutations of the same multiset.
A157612 is the version for factorials instead of superprimorials.
A317829 is the non-strict version.
A337072 is the non-strict version with squarefree factors.
A337073 is the case with squarefree factors.
A000217 counts prime factors (with multiplicity) of superprimorials.
A001055 counts factorizations.
A006939 lists superprimorials or Chernoff numbers.
A045778 counts strict factorizations.
A322583 counts factorizations into factorials.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 15 2020
EXTENSIONS
a(7)-a(13) from Andrew Howroyd, Sep 01 2020
STATUS
approved