If p is the perimeter of a right angle triangle with integral length sides, {a,b,c}, there are exactly three solutions for p = 120.

An irrational decimal fraction is created by concatenating the positive integers:

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We shall say that an n-digit number is pandigital if it makes use of all the digits 1 to n exactly once. For example, 2143 is a 4-digit pandigital and is also prime.

145 is a curious number, as 1! + 4! + 5! = 1 + 24 + 120 = 145.