The OEIS mourns the passing of Jim Simons and is grateful to the Simons Foundation for its support of research in many branches of science, including the OEIS.
The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A182301 Composite numbers that are not perfect powers and whose prime factors have an equal number of digits in decimal representation. 2

%I #7 Apr 30 2012 13:52:40

%S 6,10,12,14,15,18,20,21,24,28,30,35,40,42,45,48,50,54,56,60,63,70,72,

%T 75,80,84,90,96,98,105,108,112,120,126,135,140,143,147,150,160,162,

%U 168,175,180,187,189,192,200,209,210,221,224,240,245,247,250,252,253,270

%N Composite numbers that are not perfect powers and whose prime factors have an equal number of digits in decimal representation.

%H Arkadiusz Wesolowski, <a href="/A182301/b182301.txt">Table of n, a(n) for n = 1..10000</a>

%e 30 = 2*3*5 belongs to this sequence, since its prime factors all have one digit and 30 is not a perfect power.

%t lst1 = {}; lst2 = {}; r = 270; Do[b = IntegerDigits[FactorInteger[n]]; If[! PrimeQ[n] && Length[b[[-1, 1]]] == Length[b[[1, 1]]], AppendTo[lst1, n]], {n, 4, r}]; lst2 = Complement[lst1, Union[Flatten[Table[n^i, {i, 2, Log[2, r]}, {n, 2, r^(1/i)}]]]]; lst2

%Y Subsequence of A199009.

%K base,nonn

%O 1,1

%A _Arkadiusz Wesolowski_, Apr 23 2012

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified June 15 01:02 EDT 2024. Contains 373402 sequences. (Running on oeis4.)