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