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Composite numbers c such that pi(c) is the product of pi applied to the distinct prime factors of c.
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%I #16 Dec 16 2023 09:02:47

%S 15,21,39,57,65,91,95,133

%N Composite numbers c such that pi(c) is the product of pi applied to the distinct prime factors of c.

%C Prime numbers trivially satisfy this property and so are excluded.

%e 15 is a term since its distinct prime factors are 3,5 and pi(15) = pi(3)*pi(5).

%t Select[Range[2,10000], ! PrimeQ[#] && Times @@ PrimePi[Transpose[FactorInteger[#]][[1]]] == PrimePi[#] &]

%Y Cf. A000720, A002808, A027748, A156061, A235623.

%K nonn,fini,full

%O 1,1

%A _Tanya Khovanova_, Nov 04 2023