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 A063432 #14 May 05 2021 14:00:08
%S A063432 1,11,10,111,11,10,1111,100,11,10,11111,101,12,11,10,111111,110,20,12,
%T A063432 11,10,1111111,111,21,13,12,11,10,11111111,1000,22,20,13,12,11,10,
%U A063432 111111111,1001,100,21,14,13,12,11,10,1111111111,1010,101,22,20,14,13
%N A063432 Triangle read by rows in which k-th entry in row n is representation of n in base k, for 1 <= k <= n.
%C A063432 Representation of n in base 1 is defined to be a concatenation of n 1's.
%C A063432 It is difficult to write twenty-one in base 11 using decimal digits.
%C A063432 Representation in bases greater than 10 are written in base 10. This is really nasty! - _N. J. A. Sloane_, Dec 06 2002
%e A063432 Rows start (1), (11, 10), (111, 11, 10), (1111, 100, 11, 10), etc.
%t A063432 f[n_] := Flatten[ Append[ {FromDigits[ Table[1, {n}]] }, Table[ FromDigits[ IntegerDigits[n, i]], {i, 2, n}]]]; Flatten[ Table[ f[n], {n, 1, 10}]] (* _Robert G. Wilson v_ *)
%Y A063432 Cf. A063431.
%Y A063432 Rows are effectively the reverse of A001731, A001732, A001733, A001734, A001735, A001736, A008707, A008708, A008709, A008710, A008711, A008712, A008713, A008714, A008715, A008716, A008717, etc.
%Y A063432 Columns are truncated versions of A000042, A007088, A007089, A007090, A007091, A007092, A007093, A007094, A007095, A000027 and perhaps A055649, etc.
%Y A063432 Without the 1st column becomes A004053.
%K A063432 base,nonn,tabl
%O A063432 1,2
%A A063432 _Henry Bottomley_, Jul 20 2001