Nodes added to the frontier set each iteration

number of nodes added to frontier set each iteration increase by 2, ascending in odd numbers to n + n -1 where n is the size of the grid. the sum of the nodes added each iteration for all iterations is equal to n*n.

Iteration	Nodes In Frontier
0	1
1	3
2	5
3	7
4	9
5	11
6	13
7	15
8	17
9	19
10	21
11	23
12	25
13	27
14	29
15	31
16	33
17	35
18	37
19	39
20	41
21	43
22	45
23	47
24	49
25	51
26	53
27	55
28	57
29	59
30	61
31	63