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 A083824 #10 May 26 2021 02:38:46
%S A083824 0,1,9,8,7,6,5,4,3,2,1,11,89,79,69,59,49,39,29,19,9,109,99,78,68,58,
%T A083824 48,38,28,18,8,108,98,88,67,57,47,37,27,17,7,107,97,87,77,56,46,36,26,
%U A083824 16,6,106,96,86,76,66,45,35,25,15,5,105,95,85,75,65,55,34,24,14,4,104,94,84
%N A083824 a(n) = digit reversal of 9*n, divided by 9.
%C A083824 If n is a multiple of 10, then a(n) = a(n/10); if n is not a multiple of 10, then a(a(n)) = n.
%e A083824 a(2) = reverse(9*2)/9 = reverse(18)/9 = 81/9 = 9.
%o A083824 (PARI) {for(n=0,73,k=9*n; rev=0; while(k>0,d=divrem(k,10); k=d[1]; rev=10*rev+d[2]); print1(rev/9,","))}
%o A083824 (PARI) apply( {A083824(n)=fromdigits(Vecrev(digits(9*n)))/9}, [0..99]) \\ _M. F. Hasler_, May 21 2021
%Y A083824 Cf. A083822 (analog for 3), A083823, A083825.
%K A083824 base,easy,nonn
%O A083824 0,3
%A A083824 _Amarnath Murthy_ and Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 08 2003
%E A083824 Edited, corrected and extended by _Klaus Brockhaus_, May 11 2003
%E A083824 Minor edits and extension to offset 0 by _M. F. Hasler_, May 21 2021