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 A038396 #24 Feb 17 2024 10:30:58
%S A038396 2,42,642,8642,108642,12108642,1412108642,161412108642,18161412108642,
%T A038396 2018161412108642,222018161412108642,24222018161412108642,
%U A038396 2624222018161412108642,282624222018161412108642,30282624222018161412108642,3230282624222018161412108642
%N A038396 Concatenate first n even numbers in reverse order.
%C A038396 F. Smarandache conjectures that a(n) is never a perfect power (see link sequence 163 page 80). - _Michel Marcus_, Mar 03 2014
%D A038396 Mihaly Bencze [Beneze], L. Tutescu, Some Notions and Questions in Number Theory, Sequence 4.
%H A038396 Florentin Smarandache, <a href="http://arxiv.org/abs/math/0604019">Sequences of Numbers Involved in Unsolved Problems</a>, arXiv:math/0604019 [math.GM], 2006.
%t A038396 Join[{s = 2}, Table[s = FromDigits[Flatten[IntegerDigits[{n, s}]]], {n, 4, 26, 2}]] (* _Jayanta Basu_, Jul 14 2013 *)
%t A038396 Table[FromDigits[Flatten[IntegerDigits/@Range[2n,2,-2]]],{n,20}] (* _Harvey P. Dale_, Jun 11 2017 *)
%o A038396 (PARI) a(n) = concat(vector(n, i, Str(2*n - (2*i)+2))); \\ _Michel Marcus_, Mar 03 2014
%K A038396 nonn,base,easy
%O A038396 1,1
%A A038396 M. I. Petrescu (mipetrescu(AT)yahoo.com)
%E A038396 More terms from _Michel Marcus_, Mar 03 2014