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.
EXAMPLE
The terms together with their prime indices begin:
1: {}
3: {2}
7: {4}
9: {2,2}
10: {1,3}
13: {6}
19: {8}
21: {2,4}
27: {2,2,2}
29: {10}
30: {1,2,3}
MATHEMATICA
primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[100], Count[primeMS[#], _?(Mod[#, 4]==1&)]==Count[primeMS[#], _?(Mod[#, 4]==3&)]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Oct 12 2022
STATUS
approved