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.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..1000
EXAMPLE
We have 1993 = prime(301) = prime(7 * 43). Since 7 and 43 already belong to the sequence, so does 1993.
MATHEMATICA
ppQ[n_]:=And[PrimeQ[n], !PrimeQ[PrimePi[n]], And@@ppQ/@First/@If[n==2, {}, FactorInteger[PrimePi[n]]]];
Select[Range[1000], ppQ]
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Dec 05 2018
STATUS
approved