Numbers that are not the sum of 3 generalized 15-gonal numbers.
4, 5, 6, 7, 8, 9, 10, 11, 18, 19, 20, 21, 22, 23, 26, 29, 32, 33, 34, 35, 40, 41, 46, 47, 48, 51, 56, 59, 60, 62, 63, 65, 68, 70, 71, 73, 78, 81, 92, 93, 100, 101, 103, 104, 107, 108, 110, 114, 115, 122, 123, 130, 133, 140, 143, 144, 145, 146, 152, 155, 160
1
It appears that 87740 is the last number not representable as the sum of 3 generalized 15-gonal numbers.
T. D. Noe, Plot of 370 terms
T. D. Noe, Table of 370 terms
Eric W. Weisstein, MathWorld: Polygonal Number
(Mma) f = 15; nn = 200; 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