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 A284920 #14 Sep 08 2022 08:46:19
%S A284920 2,4,22,24,42,44,222,224,242,244,422,424,442,444,2222,2224,2242,2244,
%T A284920 2422,2424,2442,2444,4222,4224,4242,4244,4422,4424,4442,4444,22222,
%U A284920 22224,22242,22244,22422,22424,22442,22444,24222,24224,24242,24244,24422,24424
%N A284920 Numbers with digits 2 and 4 only.
%C A284920 All terms are even.
%F A284920 a(n) = 2 * A007931(n).
%t A284920 Flatten@ Array[FromDigits /@ Tuples[{2, 4}, #] &, 5] (* _Michael De Vlieger_, Apr 06 2017 *)
%o A284920 (Magma) [n: n in [1..100000] | Set(IntegerToSequence(n, 10)) subset {2, 4}]
%Y A284920 Cf. Numbers with digits 2 and k only for k = 0 - 1 and 3 - 9: A169965 (k = 0), A007931 (k = 1), A032810 (k = 3), this sequence (k = 4), A072961 (k = 5), A284632 (k = 6), A284921 (k = 7), A284922 (k = 8), A284923 (k = 9).
%K A284920 nonn,base
%O A284920 1,1
%A A284920 _Jaroslav Krizek_, Apr 05 2017