OFFSET
0,3
LINKS
Andrew Howroyd, Table of n, a(n) for n = 0..25
EXAMPLE
The a(2) = 8 chains:
12/1
12/2/1
12/3/1
12/4/1
12/6/1
12/4/2/1
12/6/2/1
12/6/3/1
MATHEMATICA
chern[n_]:=Product[Prime[i]^(n-i+1), {i, n}];
chns[n_]:=If[n==1, 1, Sum[chns[d], {d, Most[Divisors[n]]}]];
Table[chns[chern[n]], {n, 0, 3}]
PROG
(PARI) a(n)={my(sig=vector(n, i, i), m=vecsum(sig)); sum(k=0, m, prod(i=1, #sig, binomial(sig[i]+k-1, k-1))*sum(r=k, m, binomial(r, k)*(-1)^(r-k)))} \\ Andrew Howroyd, Aug 30 2020
CROSSREFS
A022915 is the maximal case.
A336571 is the case with distinct prime multiplicities.
A000005 counts divisors.
A074206 counts chains of divisors from n to 1.
A006939 lists superprimorials or Chernoff numbers.
A067824 counts divisor chains starting with n.
A253249 counts chains of divisors.
A317829 counts factorizations of superprimorials.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 13 2020
EXTENSIONS
Terms a(8) and beyond from Andrew Howroyd, Aug 30 2020
STATUS
approved