a = 1
ab = 2
abc = 4
|  a res: 4 i: 3, last: 0, start: 1, end: 7
abca = 11
|  b res: 11 i: 4, last: 1, start: 2, end: 7
abcab = 25
|  a res: 25 i: 5, last: 3, start: 11, end: 3
abcaba = 58
|  a res: 58 i: 6, last: 5, start: 58, end: 1
abcabaa = 116
|  c res: 116 i: 7, last: 2, start: 4, end: 31
abcabaac = 240
|  b res: 240 i: 8, last: 4, start: 25, end: 15
abcabaacb = 615
|  c res: 615 i: 9, last: 7, start: 240, end: 3
abcabaacbc = 1335
1335