OFFSET
1,2
COMMENTS
A prime index of n is a number m such that prime(m) divides n.
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
FORMULA
EXAMPLE
Entry A302242 describes a correspondence between positive integers and multiset multisystems. In this case it gives the following sequence of set systems.
01: {}
02: {{}}
03: {{1}}
04: {{},{}}
05: {{2}}
08: {{},{},{}}
11: {{3}}
13: {{1,2}}
16: {{},{},{},{}}
17: {{4}}
29: {{1,3}}
31: {{5}}
32: {{},{},{},{},{}}
41: {{6}}
43: {{1,4}}
47: {{2,3}}
59: {{7}}
64: {{},{},{},{},{},{}}
MATHEMATICA
primeMS[n_]:=If[n===1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[400], Or[#===1, Union[primeMS[#]]==={1}, PrimeQ[#]&&SquareFreeQ[PrimePi[#]]]&]
PROG
(PARI) ok(n)={n>>valuation(n, 2) == 1 || (isprime(n) && issquarefree(primepi(n)))} \\ Andrew Howroyd, Aug 26 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Apr 10 2018
STATUS
approved