OFFSET
1,2
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 multisystems.
001: {}
002: {{}}
003: {{1}}
004: {{},{}}
005: {{2}}
008: {{},{},{}}
011: {{3}}
016: {{},{},{},{}}
017: {{4}}
031: {{5}}
032: {{},{},{},{},{}}
041: {{6}}
059: {{7}}
064: {{},{},{},{},{},{}}
067: {{8}}
083: {{9}}
109: {{10}}
127: {{11}}
128: {{},{},{},{},{},{},{}}
MATHEMATICA
primeMS[n_]:=If[n===1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
Select[Range[1000], Or[#===1, Union[primeMS[#]]==={1}, PrimeQ[#]&&PrimeQ[PrimePi[#]]]&]
PROG
(PARI) ok(n)={n>>valuation(n, 2) == 1 || (isprime(n) && isprime(primepi(n)))} \\ Andrew Howroyd, Aug 26 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Gus Wiseman, Apr 10 2018
STATUS
approved