OFFSET
1,1
FORMULA
a(n+1) - a(n) = 3 or 4.
MATHEMATICA
tri = Table[n (n + 1)/2, {n, 0, 1000}]; t = Table[Count[tri, _?(# <= n^2 &)], {n, 0, Sqrt[tri[[-1]]]}]; Complement[Range[t[[-1]]], t] (* T. D. Noe, Mar 11 2013 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Philippe Deléham, Mar 09 2013
EXTENSIONS
Extended by T. D. Noe, Mar 11 2013
STATUS
approved