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Keywords
euler (1) math (4) number (1) triangle (2)
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Test if an integer is a triangle number Atom Feed 0

In Brief A triangular number is the sum of the n natural numbers from 1 to n.... more
# 's
 1def istriangle(n):
2 """
3 Tests if n is a triangle number.
4 Input:
5 n -- a positive integer
6 Output:
7 a positive integer indicating which triangle number in the series is n,
8 or False if n is not a triangle number
9 Examples:
10 >>> istriangle(1)
11 1
12 >>> istriangle(55)
13 10
14 >>> istriangle(7)
15 False
16 """
17 x = (math.sqrt(8*n + 1) - 1) / 2
18 if x - int(x) > 0: # if x is not an integer
19 return False
20 return int(x)

A triangular number is the sum of the n natural numbers from 1 to n.

Returns False if n is not a triangle number. If n is a triangle number, returns an integer indicating which triangle number in the series is n.