%I #5 Apr 10 2018 21:50:19
%S 1,2,3,5,6,10,11,17,22,31,34,41,59,62,67,82,83,109,118,127,134,157,
%T 166,179,191,211,218,241,254,277,283,314,331,353,358,367,382,401,422,
%U 431,461,482,509,547,554,563,566,587,599,617,662,706,709,734,739,773
%N 1, 2, prime numbers of prime index, and prime numbers of prime index times 2.
%C A prime index of n is a number m such that prime(m) divides n.
%C Also squarefree numbers whose prime indices other than 1 are equal prime numbers.
%e Entry A302242 describes a correspondence between positive integers and multiset multisystems. In this case it gives the following sequence of set systems.
%e 01: {}
%e 02: {{}}
%e 03: {{1}}
%e 05: {{2}}
%e 06: {{},{1}}
%e 10: {{},{2}}
%e 11: {{3}}
%e 17: {{4}}
%e 22: {{},{3}}
%e 31: {{5}}
%e 34: {{},{4}}
%e 41: {{6}}
%e 59: {{7}}
%e 62: {{},{5}}
%e 67: {{8}}
%e 82: {{},{6}}
%e 83: {{9}}
%t Select[Range[1000],SquareFreeQ[#]&&SameQ@@DeleteCases[primeMS[#],1]&&And@@PrimeQ/@DeleteCases[primeMS[#],1]&]
%Y Cf. A000961, A001222, A003963, A005117, A007716, A056239, A275024, A047966, A281113, A296134, A301766, A302242, A302243.
%K nonn
%O 1,2
%A _Gus Wiseman_, Apr 10 2018