Numbers that are not the sum of 3 generalized 9-gonal numbers.
4, 5, 14, 17, 22, 23, 32, 35, 50, 60, 80, 83, 88, 134, 137, 162, 168, 215, 218, 428, 623, 693, 807, 1532, 1877, 2027
1
It appears that 2027 is the last number not representable as the sum of 3 generalized 9-gonal numbers.
T. D. Noe, Plot of 26 terms
Eric W. Weisstein, MathWorld: Polygonal Number
(Mma) f = 9; nn = 50; t = Table[k ((f - 2) k - (f - 4))/2, {k, -nn, nn}]; t2 = Select[Union[Flatten[Table[a + b + c, {a, t}, {b, t}, {c, t}]]], # <= t[[-1]] &]; Complement[Range[t[[-1]]], t2]
nonn,fini
T. D. Noe, Dec 28 2015