This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A031999 #23 Aug 14 2021 02:16:41 %S A031999 1,2,3,4,5,8,9,10,12,13,14,15,16,20,21,32,36,37,40,41,42,48,52,53,56, %T A031999 57,58,60,61,62,63,64,80,84,85,128,144,148,149,160,164,165,168,169, %U A031999 170,192,208,212,213,224,228,229,232,233,234,240 %N A031999 Numbers whose base-4 digits are in nonincreasing order. %C A031999 Identical to A023760 apart from its first term. - _Charles R Greathouse IV_, May 03 2016 %H A031999 Harvey P. Dale, <a href="/A031999/b031999.txt">Table of n, a(n) for n = 1..1000</a> %t A031999 Select[Range[300], Max[Differences[IntegerDigits[#, 4]]] < 1 &] (* _Harvey P. Dale_, Apr 27 2017 *) %Y A031999 Cf. A007090, A023760, A023786 (subset). %K A031999 nonn,base %O A031999 1,2 %A A031999 _Clark Kimberling_