cp's OEIS Frontend

A280032 Composite numbers n such that the number of digits in n equals the total number of digits in the prime power factorization of n.

%I A280032 #21 Dec 29 2016 02:28:08
%S A280032 10,14,15,16,21,25,27,32,35,49,64,81,105,106,111,112,115,118,119,121,
%T A280032 122,123,129,133,134,135,141,142,145,146,147,155,158,159,160,161,162,
%U A280032 166,169,175,177,178,183,185,189,192,194,201,203,205,213,215,217,219,224,235,237,245,249,250
%N A280032 Composite numbers n such that the number of digits in n equals the total number of digits in the prime power factorization of n.
%C A280032 Suggested by A279070.
%C A280032 Primes are excluded by decree.
%C A280032 In the prime power factorization of p we write p rather than p^1.
%H A280032 Vincenzo Librandi, <a href="/A280032/b280032.txt">Table of n, a(n) for n = 1..5100</a>
%e A280032 10 = 2*5 is a term (both have 2 digits).
%e A280032 27 = 3^3 is a term (both have 2 digits).
%t A280032 ndf[n_]:=Total[IntegerLength/@Select[Flatten[FactorInteger[n]],#!=1&]];
%t A280032 Select[Range[250],!PrimeQ[#]&&IntegerLength[#]==ndf[#]&] (* _Ivan N. Ianakiev_, Dec 28 2016 *)
%Y A280032 Cf. A279070.
%K A280032 nonn,base
%O A280032 1,1
%A A280032 _N. J. A. Sloane_, Dec 27 2016
%E A280032 a(14)-a(60) from _Ivan N. Ianakiev_, Dec 28 2016