cp's OEIS Frontend

A161141 Numbers which can be expressed as the product of numbers made of only threes.

%I A161141 #11 Dec 05 2024 18:06:13
%S A161141 1,3,9,27,33,81,99,243,297,333,729,891,999,1089,2187,2673,2997,3267,
%T A161141 3333,6561,8019,8991,9801,9999,10989,19683,24057,26973,29403,29997,
%U A161141 32967,33333,35937,59049,72171,80919,88209,89991,98901,99999,107811
%N A161141 Numbers which can be expressed as the product of numbers made of only threes.
%H A161141 Robert Israel, <a href="/A161141/b161141.txt">Table of n, a(n) for n = 1..10000</a>
%e A161141 1 = empty product; 99 = 3 * 33; 1089 = 33 * 33; 999 = 3 * 333.
%p A161141 M:= 10^8: # for terms <= M
%p A161141 S:= {1}:
%p A161141 for d from 1 to ilog10(M) do
%p A161141   x:= 3/9*(10^d-1); T:= {}:
%p A161141   for s in S do
%p A161141     T:= T union {seq(s*x^i,i=1..floor(log[x](M/s)))};
%p A161141   od;
%p A161141   S:= S union T;
%p A161141 od:
%p A161141 sort(convert(S,list)); # _Robert Israel_, Dec 05 2024
%Y A161141 Cf. A084034, A161140, A161142, A161143, A161144, A161145, A161146, A161147.
%K A161141 nonn,base
%O A161141 1,2
%A A161141 _Claudio Meller_, Jun 03 2009
%E A161141 Corrected and extended by _Claudio Meller_, Jun 06 2009
%E A161141 1 added by _N. J. A. Sloane_, Dec 04 2017