OFFSET
1,2
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.
A weak run-sum of a sequence is the sum of any consecutive constant subsequence.
EXAMPLE
The prime indices of 72 are {1,1,1,2,2}, with weak runs {}, {1}, {1,1}, {1,1,1}, {2}, {2,2}, which have sums 0, 1, 2, 3, 2, 4, of which 5 are distinct, so a(72) = 5.
MATHEMATICA
Table[Length[Union@@Cases[FactorInteger[n], {p_, k_}:>Range[0, k]*PrimePi[p]]], {n, 100}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, May 23 2022
STATUS
approved