OFFSET
1,2
COMMENTS
A prime index of n is a number m such that prime(m) divides n.
EXAMPLE
49 is not in the sequence because 49 = prime(4)^2 but 4 is not squarefree.
Entry A302242 describes a correspondence between positive integers and multiset multisystems. In this case it gives the following sequence of constant set multisystems.
01: {}
02: {{}}
03: {{1}}
04: {{},{}}
05: {{2}}
08: {{},{},{}}
09: {{1},{1}}
11: {{3}}
13: {{1,2}}
16: {{},{},{},{}}
17: {{4}}
25: {{2},{2}}
27: {{1},{1},{1}}
29: {{1,3}}
31: {{5}}
32: {{},{},{},{},{}}
41: {{6}}
43: {{1,4}}
47: {{2,3}}
59: {{7}}
64: {{},{},{},{},{},{}}
MATHEMATICA
Select[Range[100], Or[#===1, PrimePowerQ[#]&&And@@SquareFreeQ/@PrimePi/@FactorInteger[#][[All, 1]]]&]
PROG
(PARI) is(n) = if(n==1, return(1), my(x=isprimepower(n)); if(x > 0, if(issquarefree(primepi(ceil(n^(1/x)))), return(1)))); 0 \\ Felix Fröhlich, Apr 10 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Apr 09 2018
STATUS
approved