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.
The median of a multiset is either the middle part (for odd length), or the average of the two middle parts (for even length).
MATHEMATICA
nn=100;
prix[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
seq=Table[If[n==1, 1, 2*Median[prix[n]]], {n, nn}];
Table[Position[seq, k][[1, 1]], {k, Count[Differences[Union[seq]], 1]}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 24 2023
STATUS
approved