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 A078262 #14 Jun 25 2025 19:32:58
%S A078262 2,33,444,5555,66666,777777,8888888,99999999,1111111110,23333333231,
%T A078262 2345555545332,244567776755433,25466789897765534,2647689001998775635,
%U A078262 274869910212099785736,28497092031222200795837,2950719304132232301805938,305172940514233242402816039
%N A078262 Sum of the forward and reverse concatenations of 1 to n.
%H A078262 Harvey P. Dale, <a href="/A078262/b078262.txt">Table of n, a(n) for n = 1..369</a>
%F A078262 a(n) = A000422(n) + A007908(n). - _Sean A. Irvine_, Jun 25 2025
%e A078262 a(3) = 123 + 321 = 444, a(10) = 12345678910 + 10987654321 = 23333333231.
%p A078262 a:= n-> parse(cat(1+n-i$i=1..n))+parse(cat($1..n)):
%p A078262 seq(a(n), n=1..18); # _Alois P. Heinz_, Jun 25 2025
%t A078262 Table[With[{c1=FromDigits[Flatten[IntegerDigits/@Range[n]]],c2= FromDigits[ Flatten[ IntegerDigits/@Range[n,1,-1]]]},c1+c2],{n,20}] (* _Harvey P. Dale_, Jul 03 2020 *)
%Y A078262 Cf. A000422, A007908, A078263.
%K A078262 base,nonn
%O A078262 1,1
%A A078262 _Amarnath Murthy_, Nov 24 2002
%E A078262 More terms from _Sascha Kurz_, Jan 04 2003