A161142 - OEIS

%I #11 Dec 05 2024 18:45:20

%S 1,4,16,44,64,176,256,444,704,1024,1776,1936,2816,4096,4444,7104,7744,

%T 11264,16384,17776,19536,28416,30976,44444,45056,65536,71104,78144,

%U 85184,113664,123904,177776,180224,195536,197136,262144,284416,312576

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

%C 64 = 4 * 4 * 4; 1936 = 44 * 44; 1776 = 4 * 444.

%H Robert Israel, <a href="/A161142/b161142.txt">Table of n, a(n) for n = 1..10000</a>

%p M:= 10^6: # for terms <= M

%p S:= {1}:

%p for d from 1 to ilog10(M) do

%p   x:= 4/9*(10^d-1); T:= {}:

%p   for s in S do

%p     T:= T union {seq(s*x^i,i=1..floor(log[x](M/s)))};

%p   od;

%p   S:= S union T;

%p od:

%p sort(convert(S,list)); # _Robert Israel_, Dec 05 2024

%Y Cf. A084034, A161140, A161141, A161143, A161144, A161145, A161146, A161147.

%K nonn,base

%O 1,2

%A _Claudio Meller_, Jun 03 2009

%E Corrected and extended by _Claudio Meller_, Jun 06 2009

%E Corrected and extended by _Claudio Meller_, Jun 27 2009

%E 1 added by _N. J. A. Sloane_, Dec 04 2017