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 A167991 #12 Mar 27 2017 03:10:29
%S A167991 2,3,4,4,4,5,6,6,6,6,6,7,8,8,8,8,8,8,8,9,10,10,10,10,10,10,10,10,10,
%T A167991 11,12,12,12,12,12,12,12,12,12,12,12,13,14,14,14,14,14,14,14,14,14,14,
%U A167991 14,14,14,15,16,16,16,16,16,16,16,16,16,16,16,16,16,16,16,17,18,18,18,18
%N A167991 Blocks of size 2n, each with 2n-1 replicas of 2n followed by 2n+1; n=1, 2, 3, ...
%C A167991 First differences of A167381.
%C A167991 The sum of the terms in block n is 4*n^2+1 = A053755(n).
%e A167991 (2, 3), (4, 4, 4, 5), (6, 6, 6, 6, 6, 7), (8, 8, 8, 8, 8, 8, 8, 9), ...
%t A167991 r[1] = Range[4];
%t A167991 r[n_] := r[n] = Range[r[n-1][[-1]]+1, r[n-1][[-1]] + (2n)^2];
%t A167991 s[n_] := Partition[r[n], Sqrt[Length[r[n]]]][[All, n]];
%t A167991 A167991 = Table[s[n], {n, 1, 9}] // Flatten // Differences (* _Jean-François Alcover_, Mar 27 2017 *)
%K A167991 nonn,easy
%O A167991 1,1
%A A167991 _Paul Curtz_, Nov 16 2009