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 A033100 #7 Nov 15 2012 04:26:31
%S A033100 0,0,1,1,1,1,2,3,4,5,7,9,12,14,19,21,24,28,33,35,40,43,49,53,57,60,68,
%T A033100 73,78,84,92,95,103,107,114,119,124,130,140,145,151,158,169,175,185,
%U A033100 191,200,209,216,222,235,242,251,260,271,278
%N A033100 Number of 3's when k is written in base b for all b and k satisfying 2<=b<=n+1, 1<=k<=n.
%t A033100 f[n_] := Count[ Flatten@ Table[ IntegerDigits[k, b], {k, n}, {b, 2, n + 1}], 3] - (n - 3); f[1] = f[2] = 0; Array[f, 56] (* _Robert G. Wilson v_, Nov 14 2012 *)
%Y A033100 Cf. A033094, A033096, A033098, A033099, A033102, A033104, A033106, A033108, A033110, A033112.
%K A033100 nonn,base
%O A033100 1,7
%A A033100 _Clark Kimberling_