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project_euler/Problem 28/sol1.py

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+from __future__ import print_function
+from math import ceil
+
+try:
+	xrange			#Python 2
+except NameError:
+	xrange = range	#Python 3
+
+def diagonal_sum(n):
+	total = 1
+
+	for i in xrange(1, int(ceil(n/2.0))):
+		odd = 2*i+1
+		even = 2*i
+		total = total + 4*odd**2 - 6*even
+
+	return total
+
+if __name__ == '__main__':
+	import sys
+
+	if len(sys.argv) == 1:
+		print(diagonal_sum(1001))
+	else:
+		try:
+			n = int(sys.argv[1])
+			diagonal_sum(n)
+		except ValueError:
+			print('Invalid entry - please enter a number')