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 A232731 #11 Sep 22 2017 19:43:01
%S A232731 4,50,450,4590,45405,454950,4544550,45454500,454495500,4545045000,
%T A232731 45449955000,454500450000,4544999550000,45450004500000,
%U A232731 454499995500000,4545000045000000,45449999955000000,454500000450000000,4544999999550000000,45450000004500000000
%N A232731 Number of numbers that yield an n-digit number after Reverse and Add!.
%C A232731 A190481 is the number of distinct n-digit numbers after Reverse and Add!.
%H A232731 Colin Barker, <a href="/A232731/b232731.txt">Table of n, a(n) for n = 1..1000</a>
%H A232731 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (10,10,-100).
%F A232731 a(1) = A232729(1), a(n) = A232729(n) + A232730(n-1), n > 1.
%F A232731 From _Colin Barker_, Mar 20 2017: (Start)
%F A232731 G.f.: x*(4 + 10*x - 90*x^2 - 10*x^3 + 5*x^4) / ((1 - 10*x)*(1 - 10*x^2)).
%F A232731 a(n) = 10*a(n-1) + 10*a(n-2) - 100*a(n-3) for n>5.
%F A232731 (End)
%t A232731 LinearRecurrence[{10,10,-100},{4,50,450,4590,45405},20] (* _Harvey P. Dale_, Sep 22 2017 *)
%o A232731 (PARI) Vec(x*(4 + 10*x - 90*x^2 - 10*x^3 + 5*x^4) / ((1 - 10*x)*(1 - 10*x^2)) + O(x^30)) \\ _Colin Barker_, Mar 20 2017
%Y A232731 Cf. A190481, A232729, A232730.
%K A232731 nonn,easy
%O A232731 1,1
%A A232731 _Lars Blomberg_, Nov 29 2013