Sum of Diagonals

diagonals_sum.py

"""
73 74 75 76 77 78 79 80 81
72 43 44 45 46 47 48 49 50
71 42 21 22 23 24 25 26 51
70 41 20  7  8  9 10 27 52
69 40 19  6  1  2 11 28 53
68 39 18  5  4  3 12 29 54
67 38 17 16 15 14 13 30 55
66 37 36 35 34 33 32 31 56
65 64 63 62 61 60 59 58 57
"""

size = 1001
ia, ib, ic, id = 10, 12, 14, 16
a, b, c, d = 3, 5, 7, 9
s = 1
for i in range(0, size // 2):
    s += sum([a, b, c, d])
    a, b, c, d = a + ia, b + ib, c + ic, d + id
    ia, ib, ic, id = ia + 8, ib + 8, ic + 8, id + 8
print(s)