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.
EXAMPLE
The terms together with their prime indices begin:
10: {1,3}
28: {1,1,4}
30: {1,2,3}
39: {2,6}
84: {1,1,2,4}
88: {1,1,1,5}
90: {1,2,2,3}
100: {1,1,3,3}
115: {3,9}
171: {2,2,8}
208: {1,1,1,1,6}
252: {1,1,2,2,4}
255: {2,3,7}
259: {4,12}
264: {1,1,1,2,5}
MATHEMATICA
prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[100], Mean[prix[#]]==2*Min[prix[#]]&]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, May 29 2023
STATUS
approved