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 A084021 #17 Sep 17 2019 12:45:17
%S A084021 0,8,14,18,20,20,18,14,8,0,890,968,1044,1118,1190,1260,1328,1394,1458,
%T A084021 1520,1580,1638,1694,1748,1800,1850,1898,1944,1988,2030,2070,2108,
%U A084021 2144,2178,2210,2240,2268,2294,2318,2340,2360,2378,2394,2408,2420,2430,2438
%N A084021 Product of n and its 9's complement.
%C A084021 There are infinitely many nonzero squares in this sequence; for example a(10^(4n) - 10^(2n)) = (10^n*(10^(2n)-1))^2. - _David Wasserman_, Dec 07 2004
%H A084021 Seiichi Manyama, <a href="/A084021/b084021.txt">Table of n, a(n) for n = 0..9999</a>
%F A084021 a(n) = n*(10^d - 1 - n), where d is the number of digits in n.
%F A084021 a(n) = n*A061601(n). - _David Wasserman_, Dec 07 2004
%o A084021 (PARI) {a(n) = n*(10^length(Str(n))-1-n)} \\ _Seiichi Manyama_, Sep 15 2019
%Y A084021 Cf. A061601.
%K A084021 base,easy,nonn
%O A084021 0,2
%A A084021 _Amarnath Murthy_, May 23 2003
%E A084021 More terms from _David Wasserman_, Dec 07 2004
%E A084021 a(0)=0 prepended by _Seiichi Manyama_, Sep 15 2019