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

1,2

Comments

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

Links

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

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

Crossrefs

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

Sequence in context: A034131 A183536 A320100 * A259013 A212960 A217873

Adjacent sequences: A161139 A161140 A161141 * A161143 A161144 A161145

Keyword

nonn,base

Author

Claudio Meller, Jun 03 2009

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

Status

approved