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 A082944 #20 Jan 06 2022 20:42:14
%S A082944 121,242,363,484,515,636,757,878,999,10201,11411,12621,13831,14141,
%T A082944 15351,16561,17771,18981,19291,20402,21612,22822,23132,24342,25552,
%U A082944 26762,27972,28282,29492,30603
%N A082944 a(n) = concatenate(n, A010888(2*n), reverse(n)), where A010888 = digital root.
%C A082944 The central digit A010888(2*n) cyclically repeats the nine digits (2, 4, 6, 8, 1, 3, 5, 7, 9) in this order.
%C A082944 The sum of the digits of n plus the digits of the reverse of n is always simply 2 times the sum of the digits of n. - _Harvey P. Dale_, Aug 12 2019
%D A082944 Amarnath Murthy
%e A082944 For a(17): 1+7+7+1 = 16. 1+6 = 7. Thus the center digit is 7 and a(17) = 17771.
%e A082944 For a(23): 2+3+3+2 = 10. 1+0 = 1. Thus the center digit is 1 and a(23) = 23132.
%t A082944 nxt[n_]:=Module[{idn=IntegerDigits[n],b,c},b=NestWhile[Total[IntegerDigits[ # ]]&, 2 Total[idn],#>9&];c=Reverse[idn];FromDigits[Join[idn,{b},c]]]; Table[ nxt[n],{n,20}] (* _Harvey P. Dale_, Aug 12 2019 *)
%o A082944 (PARI) A082944(n)=fromdigits(concat([digits(n), (2*n-1)%9+1, Vecrev(digits(n))])) \\ Cf. A010888. - _R. J. Cano_, Jan 05 2022
%Y A082944 Cf. A010888 (digital root), A004086 (read n backwards: trailing zeros are lost - but not in this sequence here).
%K A082944 easy,nonn,base
%O A082944 1,1
%A A082944 Meenakshi Srikanth (menakan_s(AT)yahoo.com), May 06 2003
%E A082944 Definition, comment and example corrected by _M. F. Hasler_, Jan 05 2022