OFFSET
0,2
COMMENTS
Partial sums of A214856.
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..10000
FORMULA
a(n) = floor((1 + sqrt(1+8*n^2))/2). - Ralf Stephan, Jan 30 2014
EXAMPLE
0, 1, 3, 6 are in interval [0, 9], a(3) = 4.
0, 1, 3, 6, 10, 15 are in interval [0, 16], a(4) = 6.
MATHEMATICA
nn = 100; tri = Table[n (n + 1)/2, {n, 0, nn}]; Table[Count[tri, _?(# <= n^2 &)], {n, 0, Sqrt[tri[[-1]]]}] (* T. D. Noe, Mar 11 2013 *)
Table[Floor[(Sqrt[8*n^2+1]-1)/2]+1, {n, 0, 80}] (* Harvey P. Dale, Oct 14 2014 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Philippe Deléham, Mar 09 2013
STATUS
approved