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}
5: {3}
6: {1,2}
7: {4}
11: {5}
12: {1,1,2}
13: {6}
14: {1,4}
17: {7}
18: {1,2,2}
19: {8}
23: {9}
24: {1,1,1,2}
MATHEMATICA
nn=1000;
prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
seq=Table[If[n==1, 1, Mean[prix[n]]], {n, nn}];
Select[Range[nn], FreeQ[seq[[Range[#-1]]], seq[[#]]]&]
CROSSREFS
A316413 lists numbers whose prime indices have integer mean.
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 24 2023
STATUS
approved