cp's OEIS Frontend

A330948 Nonprime numbers whose prime indices are not all prime numbers.

%I A330948 #6 Jan 14 2020 22:17:21
%S A330948 4,6,8,10,12,14,16,18,20,21,22,24,26,28,30,32,34,35,36,38,39,40,42,44,
%T A330948 46,48,49,50,52,54,56,57,58,60,62,63,64,65,66,68,69,70,72,74,76,77,78,
%U A330948 80,82,84,86,87,88,90,91,92,94,95,96,98,100,102,104,105,106
%N A330948 Nonprime numbers whose prime indices are not all prime numbers.
%C A330948 A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
%e A330948 The sequence of terms together with their prime indices of prime indices begins:
%e A330948    4: {{},{}}
%e A330948    6: {{},{1}}
%e A330948    8: {{},{},{}}
%e A330948   10: {{},{2}}
%e A330948   12: {{},{},{1}}
%e A330948   14: {{},{1,1}}
%e A330948   16: {{},{},{},{}}
%e A330948   18: {{},{1},{1}}
%e A330948   20: {{},{},{2}}
%e A330948   21: {{1},{1,1}}
%e A330948   22: {{},{3}}
%e A330948   24: {{},{},{},{1}}
%e A330948   26: {{},{1,2}}
%e A330948   28: {{},{},{1,1}}
%e A330948   30: {{},{1},{2}}
%e A330948   32: {{},{},{},{},{}}
%e A330948   34: {{},{4}}
%e A330948   35: {{2},{1,1}}
%e A330948   36: {{},{},{1},{1}}
%e A330948   38: {{},{1,1,1}}
%t A330948 Select[Range[100],!PrimeQ[#]&&!And@@PrimeQ/@PrimePi/@First/@If[#==1,{},FactorInteger[#]]&]
%Y A330948 Complement in A330945 of A000040.
%Y A330948 Complement in A018252 of A076610.
%Y A330948 The restriction to odd terms is A330949.
%Y A330948 Nonprime numbers n such that A330944(n) > 0.
%Y A330948 Taking odds instead of nonprimes gives A330946.
%Y A330948 The number of prime prime indices is given by A257994.
%Y A330948 Primes of prime index are A006450.
%Y A330948 Primes of nonprime index are A007821.
%Y A330948 Products of primes of nonprime index are A320628.
%Y A330948 The set S of numbers whose prime indices do not all belong to S is A324694.
%Y A330948 Cf. A000720, A001222, A056239, A112798, A302242, A320629, A320633, A330943, A330947.
%K A330948 nonn
%O A330948 1,1
%A A330948 _Gus Wiseman_, Jan 13 2020