A280032 - OEIS

%I #21 Dec 29 2016 02:28:08

%S 10,14,15,16,21,25,27,32,35,49,64,81,105,106,111,112,115,118,119,121,

%T 122,123,129,133,134,135,141,142,145,146,147,155,158,159,160,161,162,

%U 166,169,175,177,178,183,185,189,192,194,201,203,205,213,215,217,219,224,235,237,245,249,250

%N 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 Suggested by A279070.

%C Primes are excluded by decree.

%C In the prime power factorization of p we write p rather than p^1.

%H Vincenzo Librandi, <a href="/A280032/b280032.txt">Table of n, a(n) for n = 1..5100</a>

%e 10 = 2*5 is a term (both have 2 digits).

%e 27 = 3^3 is a term (both have 2 digits).

%t ndf[n_]:=Total[IntegerLength/@Select[Flatten[FactorInteger[n]],#!=1&]];

%t Select[Range[250],!PrimeQ[#]&&IntegerLength[#]==ndf[#]&] (* _Ivan N. Ianakiev_, Dec 28 2016 *)

%Y Cf. A279070.

%K nonn,base

%O 1,1

%A _N. J. A. Sloane_, Dec 27 2016

%E a(14)-a(60) from _Ivan N. Ianakiev_, Dec 28 2016