cp's OEIS Frontend

A161142 Numbers which can be expressed as the product of numbers made of only fours.

%I A161142 #11 Dec 05 2024 18:45:20
%S A161142 1,4,16,44,64,176,256,444,704,1024,1776,1936,2816,4096,4444,7104,7744,
%T A161142 11264,16384,17776,19536,28416,30976,44444,45056,65536,71104,78144,
%U A161142 85184,113664,123904,177776,180224,195536,197136,262144,284416,312576
%N A161142 Numbers which can be expressed as the product of numbers made of only fours.
%C A161142 64 = 4 * 4 * 4; 1936 = 44 * 44; 1776 = 4 * 444.
%H A161142 Robert Israel, <a href="/A161142/b161142.txt">Table of n, a(n) for n = 1..10000</a>
%p A161142 M:= 10^6: # for terms <= M
%p A161142 S:= {1}:
%p A161142 for d from 1 to ilog10(M) do
%p A161142   x:= 4/9*(10^d-1); T:= {}:
%p A161142   for s in S do
%p A161142     T:= T union {seq(s*x^i,i=1..floor(log[x](M/s)))};
%p A161142   od;
%p A161142   S:= S union T;
%p A161142 od:
%p A161142 sort(convert(S,list)); # _Robert Israel_, Dec 05 2024
%Y A161142 Cf. A084034, A161140, A161141, A161143, A161144, A161145, A161146, A161147.
%K A161142 nonn,base
%O A161142 1,2
%A A161142 _Claudio Meller_, Jun 03 2009
%E A161142 Corrected and extended by _Claudio Meller_, Jun 06 2009
%E A161142 Corrected and extended by _Claudio Meller_, Jun 27 2009
%E A161142 1 added by _N. J. A. Sloane_, Dec 04 2017