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

1, 4, 16, 44, 64, 176, 256, 444, 704, 1024, 1776, 1936, 2816, 4096, 4444, 7104, 7744, 11264, 16384, 17776, 19536, 28416, 30976, 44444, 45056, 65536, 71104, 78144, 85184, 113664, 123904, 177776, 180224, 195536, 197136, 262144, 284416, 312576

Offset: 1

Author

Claudio Meller, Jun 03 2009

Keywords

• nonn
• base

Comments

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

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

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

Programs

Maple

M:= 10^6: # for terms <= M
S:= {1}:
for d from 1 to ilog10(M) do
  x:= 4/9*(10^d-1); T:= {}:
  for s in S do
    T:= T union {seq(s*x^i,i=1..floor(log[x](M/s)))};
  od;
  S:= S union T;
od:
sort(convert(S,list)); # Robert Israel, Dec 05 2024

Extensions

Corrected and extended by Claudio Meller, Jun 06 2009

Corrected and extended by Claudio Meller, Jun 27 2009

1 added by N. J. A. Sloane, Dec 04 2017