OFFSET
1,2
LINKS
Ray Chandler, Table of n, a(n) for n = 1..2500
FORMULA
Conjectures from Chai Wah Wu, Jun 22 2016: (Start)
a(n) = n*(n+1)/2 - 1 for n >= 9.
a(n) = 3*a(n-1) - 3*a(n-2) + a(n-3) for n > 11.
G.f.: x*(-x^10 + 2*x^9 - x^8 - 2*x^7 + 4*x^6 - x^5 - 2*x^3 + x - 1)/(x - 1)^3. (End)
MATHEMATICA
nmax = 50; d = {1}; a1 = {};
Do[
n0s = Table[0, {n}];
d = Join[d, n0s, n0s] + Join[n0s, d, n0s] + Join[n0s, n0s, d];
AppendTo[a1, Length[Union[d]]];
, {n, nmax}];
a1 (* Ray Chandler, Mar 26 2014 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved