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 weighted sum of a sequence (y_1,...,y_k) is Sum_{i=1..k} i*y_i.
EXAMPLE
The terms together with their prime indices begin:
1: {}
2: {1}
3: {2}
4: {1,1}
6: {1,2}
8: {1,1,1}
10: {1,3}
12: {1,1,2}
16: {1,1,1,1}
18: {1,2,2}
19: {8}
24: {1,1,1,2}
27: {2,2,2}
32: {1,1,1,1,1}
36: {1,1,2,2}
43: {14}
48: {1,1,1,1,2}
MATHEMATICA
nn=100;
primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
ots[y_]:=Sum[i*y[[i]], {i, Length[y]}];
seq=Table[ots[Reverse[primeMS[n]]], {n, 1, nn}];
Select[Range[nn], FreeQ[seq[[Range[#-1]]], seq[[#]]]&]
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 15 2023
STATUS
approved