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 A248422 #25 Sep 08 2022 08:46:10
%S A248422 22,44,66,88,1010,1212,1414,1616,1818,2020,2222,2424,2626,2828,3030,
%T A248422 3232,3434,3636,3838,4040,4242,4444,4646,4848,5050,5252,5454,5656,
%U A248422 5858,6060,6262,6464,6666,6868,7070,7272,7474,7676,7878,8080,8282,8484,8686,8888,9090,9292,9494,9696,9898,100100
%N A248422 Even integers concatenated with themselves.
%C A248422 Bisection of A020338.
%H A248422 Harvey P. Dale, <a href="/A248422/b248422.txt">Table of n, a(n) for n = 1..1000</a>
%F A248422 a(n) = 2*n*10^ceiling(log_10(2*n)) + 2*n. - _Tom Edgar_, Oct 21 2014
%t A248422 FromDigits[Flatten[IntegerDigits/@#]]&/@Partition[With[{c=2*Range[ 50]}, Riffle[c,c]],2] (* or *) Table[n*10^IntegerLength[n]+n,{n,2,100,2}] (* _Harvey P. Dale_, Jun 11 2019 *)
%o A248422 (PARI) a(n) = eval(concat(Str(2*n), Str(2*n))); \\ _Michel Marcus_, Oct 06 2014
%o A248422 (Magma) [Seqint(Intseq(n) cat Intseq(n)): n in [2..100 by 2]]; // _Vincenzo Librandi_, Oct 21 2014
%Y A248422 Cf. A020338.
%K A248422 nonn,base
%O A248422 1,1
%A A248422 _Lev Krasnovsky_, Oct 06 2014