cp's OEIS Frontend

A302478 Products of prime numbers of squarefree index.

%I A302478 #10 Aug 27 2018 01:52:57
%S A302478 1,2,3,4,5,6,8,9,10,11,12,13,15,16,17,18,20,22,24,25,26,27,29,30,31,
%T A302478 32,33,34,36,39,40,41,43,44,45,47,48,50,51,52,54,55,58,59,60,62,64,65,
%U A302478 66,67,68,72,73,75,78,79,80,81,82,83,85,86,87,88,90,93,94
%N A302478 Products of prime numbers of squarefree index.
%C A302478 A prime index of n is a number m such that prime(m) divides n.
%H A302478 Andrew Howroyd, <a href="/A302478/b302478.txt">Table of n, a(n) for n = 1..1000</a>
%e A302478 Entry A302242 describes a correspondence between positive integers and multiset multisystems. In this case it gives the following sequence of set multisystems.
%e A302478 01:  {}
%e A302478 02:  {{}}
%e A302478 03:  {{1}}
%e A302478 04:  {{},{}}
%e A302478 05:  {{2}}
%e A302478 06:  {{},{1}}
%e A302478 08:  {{},{},{}}
%e A302478 09:  {{1},{1}}
%e A302478 10:  {{},{2}}
%e A302478 11:  {{3}}
%e A302478 12:  {{},{},{1}}
%e A302478 13:  {{1,2}}
%e A302478 15:  {{1},{2}}
%e A302478 16:  {{},{},{},{}}
%e A302478 17:  {{4}}
%e A302478 18:  {{},{1},{1}}
%e A302478 20:  {{},{},{2}}
%e A302478 22:  {{},{3}}
%e A302478 24:  {{},{},{},{1}}
%e A302478 25:  {{2},{2}}
%e A302478 26:  {{},{1,2}}
%e A302478 27:  {{1},{1},{1}}
%e A302478 29:  {{1,3}}
%e A302478 30:  {{},{1},{2}}
%e A302478 31:  {{5}}
%e A302478 32:  {{},{},{},{},{}}
%t A302478 Select[Range[100],Or[#===1,And@@SquareFreeQ/@PrimePi/@FactorInteger[#][[All,1]]]&]
%o A302478 (PARI) ok(n)={!#select(p->!issquarefree(primepi(p)), factor(n)[,1])} \\ _Andrew Howroyd_, Aug 26 2018
%Y A302478 Cf. A000961, A001222, A003963, A005117, A007716, A050320, A056239, A063834, A076610, A270995, A275024, A281113, A296119, A301753, A302242, A302243, A302491.
%K A302478 nonn
%O A302478 1,2
%A A302478 _Gus Wiseman_, Apr 08 2018