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 A004155 #16 Oct 24 2023 20:33:32
%S A004155 1,3,5,7,9,2,4,6,8,10,3,5,7,9,11,4,6,8,10,12,5,7,9,11,13,6,8,10,12,14,
%T A004155 7,9,11,13,15,8,10,12,14,16,9,11,13,15,17,10,12,14,16,18,2,4,6,8,10,3,
%U A004155 5,7,9,11,4,6,8,10,12,5
%N A004155 Sum of digits of n-th odd number.
%H A004155 G. C. Greubel, <a href="/A004155/b004155.txt">Table of n, a(n) for n = 0..10000</a>
%F A004155 a(n) = 2n - 1 - 9*Sum_{k=1..1+floor(log_10(2n-1))} floor( (n-1)/(5*10^(k-1)) ). - _Anthony Browne_, Jun 18 2016
%F A004155 a(n) = A004092(n+5). - _G. C. Greubel_, Jun 19 2016
%t A004155 Table[Sum[DigitCount[2*n + 1][[i]]*i, {i, 9}], {n, 0, 100}] (* _G. C. Greubel_, Jun 19 2016 *)
%o A004155 (PARI) a(n)=sumdigits(2*n+1) \\ _Charles R Greathouse IV_, Jun 19 2016
%Y A004155 Cf. A004092, A007953.
%K A004155 nonn,base,easy
%O A004155 0,2
%A A004155 _N. J. A. Sloane_