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 A040163 #26 Apr 24 2024 12:59:58
%S A040163 0,0,0,0,0,0,0,0,0,1,0,1,2,3,4,5,6,7,8,2,1,0,1,2,3,4,5,6,7,3,2,1,0,1,
%T A040163 2,3,4,5,6,4,3,2,1,0,1,2,3,4,5,5,4,3,2,1,0,1,2,3,4,6,5,4,3,2,1,0,1,2,
%U A040163 3,7,6,5,4,3,2,1,0,1,2,8,7,6,5,4,3,2,1,0,1,9,8,7,6,5,4,3,2,1,0,1,0,1,2,3,4,5
%N A040163 a(n) is the absolute value of (the first digit of n minus the last digit of n).
%H A040163 David F. Marrs, <a href="/A040163/b040163.txt">Table of n, a(n) for n = 1..10000</a>
%F A040163 a(n) = abs(floor(n / 10 ^ floor(log_10(n))) - (n - floor(n / 10) * 10)) - _David F. Marrs_, Oct 14 2018
%e A040163 a(371) = abs(3 - 1) = 2.
%e A040163 a(567) = abs(5 - 7) = 2.
%t A040163 Array[Abs[First@ # - Last@ #] &@ IntegerDigits@ # &, 106] (* _Michael De Vlieger_, Oct 15 2018 *)
%o A040163 (PARI) a(n) = my(digs = digits(n)); abs(digs[1] - digs[#digs]); \\ _Michel Marcus_, Sep 27 2013
%o A040163 (PARI) apply( {A040163(n)=abs(n\10^logint(n+!n,10)-n%10)}, [0..111]) \\ _M. F. Hasler_, Apr 22 2024
%o A040163 (Python) for n in range(1,51): print(abs(int(str(n)[0])-int(str(n)[-1]))) # _David F. Marrs_, Oct 14 2018
%Y A040163 Cf. A000030 (first digit of n), A010879 (last digit of n).
%Y A040163 Cf. A037904, A040114, A040115, A040997.
%K A040163 nonn,base
%O A040163 1,13
%A A040163 _Felice Russo_