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 A122640 #15 Jul 04 2022 11:02:25
%S A122640 2,4,6,8,5,8,11,14,17,20,24,28,32,36,45,50,55,60,65,80,86,92,98,104,
%T A122640 125,132,139,146,153,180,188,196,204,212,245,254,263,272,281,320,330,
%U A122640 340,350,360,405,416,427,438,449,2500,2603,2708,2815,2924,3080,3194,3310,3428,3548
%N A122640 a(n) = {2n}_n.
%C A122640 See A122618 for notation.
%H A122640 Michael De Vlieger, <a href="/A122640/b122640.txt">Table of n, a(n) for n = 1..10000</a>
%p A122640 a:= n-> (l-> add(l[i]*n^(i-1), i=1..nops(l)))(convert(2*n, base, 10)):
%p A122640 seq(a(n), n=1..60); # _Alois P. Heinz_, Jul 04 2022
%t A122640 Array[FromDigits[IntegerDigits[2 #], #] &, 59] (* _Michael De Vlieger_, Jul 04 2022 *)
%o A122640 (PARI) a(n) = fromdigits(digits(2*n),max(2,n)); \\ _Kevin Ryde_, Jul 04 2022
%Y A122640 Cf. A122618 (n_n).
%K A122640 nonn,base,easy
%O A122640 1,1
%A A122640 _N. J. A. Sloane_, Sep 21 2006