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 A232729 #28 Oct 27 2022 10:21:23 %S A232729 4,45,405,4095,40500,405450,4050000,40504500,405000000,4050045000, %T A232729 40500000000,405000450000,4050000000000,40500004500000, %U A232729 405000000000000,4050000045000000,40500000000000000,405000000450000000,4050000000000000000,40500000004500000000,405000000000000000000 %N A232729 Number of n-digit numbers that yield an n-digit number after Reverse and Add. %H A232729 Robert Israel, <a href="/A232729/b232729.txt">Table of n, a(n) for n = 1..990</a> %H A232729 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (10,10,-100). %F A232729 a(n) + A232730(n) = 9*10^(n-1). %F A232729 a(1) = 4, a(3) = 405, a(2k+1) = 100*a(2k-1), k > 1. %F A232729 a(2) = 45, a(4) = 4095, a(2k) = 110*a(2k-2) - 1000*a(2k-4), k > 2. %F A232729 From _Colin Barker_, Apr 21 2016: (Start) %F A232729 a(n) = 10*a(n-1)+10*a(n-2)-100*a(n-3) for n>4. %F A232729 G.f.: x*(4+5*x-85*x^2-5*x^3) / ((1-10*x)*(1-10*x^2)). (End) %F A232729 E.g.f.: (81*cosh(10*x) + 90*cosh(sqrt(10)*x) + 81*sinh(10*x) - 10*x - 171)/200. - _Stefano Spezia_, Oct 27 2022 %e A232729 There are 4 1-digit numbers (1,2,3,4) that yield a 1-digit number (2,4,6,8), so a(1)=4. %o A232729 (PARI) Vec(x*(4+5*x-85*x^2-5*x^3)/((1-10*x)*(1-10*x^2)) + O(x^50)) \\ _Colin Barker_, Apr 22 2016 %Y A232729 Cf. A232730, A232731. %K A232729 nonn,base,easy %O A232729 1,1 %A A232729 _Lars Blomberg_, Nov 29 2013