-64
-64 - 1 = -63
It is: 64-1 = 63
63 minus 21 is 42.
It is: 63-4 = 59
3968. The formula is the starting number squared, minus 1 (2*2-1=3...3*3-1=8....8*8-1=63..... 63*63-1=3968)
100 - 63 = 37
-16 - 63 = -79
63 - 18 = 45
63 - 37 = 26
63 - 10 = 53
111 - 63 = 48
45 - 63 = -18