OFFSET
1,6
COMMENTS
An interval is a set of positive integers with all differences of adjacent elements equal to 1.
A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
LINKS
EXAMPLE
The a(n) multiset partitions for n = 6, 30, 36, 90, 180:
{12} {123} {12}{12} {12}{23} {12}{123}
{1}{2} {1}{23} {1}{2}{12} {2}{123} {1}{12}{23}
{3}{12} {1}{1}{2}{2} {1}{2}{23} {1}{2}{123}
{1}{2}{3} {2}{3}{12} {3}{12}{12}
{1}{2}{2}{3} {1}{1}{2}{23}
{1}{2}{3}{12}
{1}{1}{2}{2}{3}
The a(n) factorizations for n = 6, 30, 36, 90, 180:
(6) (30) (6*6) (3*30) (6*30)
(2*3) (5*6) (2*3*6) (6*15) (5*6*6)
(2*15) (2*2*3*3) (3*5*6) (2*3*30)
(2*3*5) (2*3*15) (2*6*15)
(2*3*3*5) (2*3*5*6)
(2*2*3*15)
(2*2*3*3*5)
MATHEMATICA
primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
chQ[y_]:=Or[Length[y]<=1, Union[Differences[y]]=={1}];
Table[Length[Select[facs[n], And@@chQ/@primeMS/@#&]], {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 08 2022
STATUS
approved