%I #7 Dec 15 2017 17:36:28
%S 1,1,2,1,2,2,1,2,2,2,2,2,2,3,3,2,2,3,3,3,3,2,3,3,3,3,3,4,3,3,3,3,4,4,
%T 4,4,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,5,5,5,4,4,4,4,5,5,5,5,5,5,5,4,5,
%U 5,5,5,5,5,5,5,5,6,6,5,5,5,5,5,5,5,6,6,6,6,6,6,5,5,5,6,6,6,6,6,6,6,6,6,6,7
%N Number of triangular numbers between n and 2n (inclusive).
%t With[{trnos=Accumulate[Range[100]]},Table[Count[trnos,_?(n<=#<=2n&)],{n,110}]] (* _Harvey P. Dale_, Jul 23 2013 *)
%K easy,nonn
%O 1,3
%A Amarnath Murthy, _Jason Earls_, Jul 22 2003