cp's OEIS Frontend

A320633 Composite numbers whose prime indices are also composite.

%I A320633 #4 Oct 18 2018 08:50:37
%S A320633 49,91,133,161,169,203,247,259,299,301,329,343,361,371,377,427,437,
%T A320633 481,497,511,529,551,553,559,611,623,637,667,679,689,703,707,721,749,
%U A320633 791,793,817,841,851,893,917,923,931,949,959,973,989,1007,1027,1043,1057
%N A320633 Composite numbers whose prime indices are also composite.
%C A320633 A prime index of n is a number m such that prime(m) divides n.
%e A320633 The sequence of terms begins:
%e A320633    49 = prime(4)^2
%e A320633    91 = prime(4)*prime(6)
%e A320633   133 = prime(4)*prime(8)
%e A320633   161 = prime(4)*prime(9)
%e A320633   169 = prime(6)^2
%e A320633   203 = prime(4)*prime(10)
%e A320633   247 = prime(6)*prime(8)
%e A320633   259 = prime(4)*prime(12)
%e A320633   299 = prime(6)*prime(9)
%e A320633   301 = prime(4)*prime(14)
%e A320633   329 = prime(4)*prime(15)
%e A320633   343 = prime(4)^3
%e A320633   361 = prime(8)^2
%e A320633   371 = prime(4)*prime(16)
%e A320633   377 = prime(6)*prime(10)
%e A320633   427 = prime(4)*prime(18)
%e A320633   437 = prime(8)*prime(9)
%e A320633   481 = prime(6)*prime(12)
%e A320633   497 = prime(4)*prime(20)
%e A320633   511 = prime(4)*prime(21)
%e A320633   529 = prime(9)^2
%e A320633   551 = prime(8)*prime(10)
%e A320633   553 = prime(4)*prime(22)
%e A320633   559 = prime(6)*prime(14)
%e A320633   611 = prime(6)*prime(15)
%e A320633   623 = prime(4)*prime(24)
%e A320633   637 = prime(4)^2*prime(6)
%t A320633 Select[Range[2,1000],And[OddQ[#],!PrimeQ[#],And@@Not/@PrimeQ/@PrimePi/@First/@FactorInteger[#]]&]
%Y A320633 Cf. A000040, A006450, A007821, A018252, A050370, A056239, A076610, A112798, A302242, A302478, A320533, A320628, A320629.
%K A320633 nonn
%O A320633 1,1
%A A320633 _Gus Wiseman_, Oct 18 2018