Numbers that are not the sum of 3 generalized 11-gonal numbers.
4, 5, 6, 7, 14, 15, 18, 21, 28, 29, 35, 40, 43, 45, 48, 54, 57, 64, 65, 72, 78, 79, 93, 100, 115, 123, 129, 135, 140, 151, 158, 159, 165, 170, 175, 186, 187, 231, 240, 263, 273, 288, 306, 309, 323, 330, 350, 353, 360, 372, 381, 438, 480, 489, 495, 519, 555
1
It appears that 18180 is the last number not representable as the sum of 3 generalized 11-gonal numbers.
T. D. Noe, Plot of 94 terms
T. D. Noe, Table of 94 terms
Eric W. Weisstein, MathWorld: Polygonal Number
(Mma) f = 11; nn = 100; 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