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 sequence of terms together with their prime indices begins:
1: {}
21: {2,4}
57: {2,8}
115: {3,9}
133: {4,8}
145: {3,10}
159: {2,16}
371: {4,16}
393: {2,32}
399: {2,4,8}
515: {3,27}
535: {3,28}
565: {3,30}
667: {9,10}
803: {5,21}
869: {5,22}
917: {4,32}
933: {2,64}
1007: {8,16}
1067: {5,25}
MATHEMATICA
primeMS[n_]:=If[n==1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[1000], !PrimeQ[#]&&SquareFreeQ[#]&&SameQ@@Mean/@primeMS/@primeMS[#]&];
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Sep 30 2019
STATUS
approved