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 A056965 #40 Dec 20 2023 09:48:28
%S A056965 0,0,0,0,0,0,0,0,0,0,9,0,-9,-18,-27,-36,-45,-54,-63,-72,18,9,0,-9,-18,
%T A056965 -27,-36,-45,-54,-63,27,18,9,0,-9,-18,-27,-36,-45,-54,36,27,18,9,0,-9,
%U A056965 -18,-27,-36,-45,45,36,27,18,9,0,-9,-18,-27,-36,54,45,36,27,18,9,0,-9,-18,-27,63,54,45,36,27,18,9,0,-9,-18,72,63,54
%N A056965 a(n) = n - (reversal of digits of n).
%C A056965 a(n) is a multiple of 9.
%H A056965 Reinhard Zumkeller, <a href="/A056965/b056965.txt">Table of n, a(n) for n = 0..10000</a>
%H A056965 <a href="/index/K#Kaprekar_map">Index entries for the Kaprekar map</a>
%F A056965 a(n) = n - A004086(n) = 2*n - A056964(n).
%e A056965 a(17) = 17 - 71 = -54.
%p A056965 a:= n-> (s-> n-parse(cat(s[-i]$i=1..length(s))))(""||n):
%p A056965 seq(a(n), n=0..82); # _Alois P. Heinz_, Jul 11 2021
%t A056965 Table[n - FromDigits[Reverse[IntegerDigits[n]]], {n, 0, 82}] (* _Jayanta Basu_, Jul 11 2013 *)
%o A056965 (Haskell)
%o A056965 a056965 n = n - a004086 n -- _Reinhard Zumkeller_, Sep 17 2013
%o A056965 (Python)
%o A056965 def a(n): return n - int(str(n)[::-1]) # _Osman Mustafa Quddusi_, Jul 11 2021
%o A056965 (PARI) a(n) = n - fromdigits(Vecrev(digits(n))); \\ _Michel Marcus_, Dec 20 2023
%Y A056965 Cf. A004086, A056964, A068396, A151949, A265326.
%K A056965 base,sign,look
%O A056965 0,11
%A A056965 _Henry Bottomley_, Jul 18 2000