OFFSET
1,1
COMMENTS
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.
Every sequence can be uniquely split into a sequence of non-overlapping runs. For example, the runs of (2,2,1,1,1,3,2,2) are ((2,2),(1,1,1),(3),(2,2)), with sums (4,3,3,4).
EXAMPLE
The terms together with their prime indices begin:
12: {1,1,2}
40: {1,1,1,3}
60: {1,1,2,3}
63: {2,2,4}
84: {1,1,2,4}
112: {1,1,1,1,4}
120: {1,1,1,2,3}
126: {1,2,2,4}
132: {1,1,2,5}
144: {1,1,1,1,2,2}
156: {1,1,2,6}
204: {1,1,2,7}
228: {1,1,2,8}
252: {1,1,2,2,4}
276: {1,1,2,9}
280: {1,1,1,3,4}
300: {1,1,2,3,3}
315: {2,2,3,4}
MATHEMATICA
Select[Range[100], !UnsameQ@@Cases[FactorInteger[#], {p_, k_}:>k*PrimePi[p]]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jun 04 2022
STATUS
approved