A number n is practical if all smaller numbers can be written as a sum of the proper divisors of n. The number 24 is practical because its proper divisors are 1, 2, 3, 4, 6, 8, and 12 and for example
5 = 4+1, 7 = 4+3, 9 = 6+3, 10 = 8+2, 11 = 8+3, 13 = 12+1, 14 = 12+2, 15 = 12+3, 16 = 12+4,
17 = 12+4+1, 18 = 12+6, 19 = 12+3+4, 20 = 12+8, 21 = 12+8+1, 22 = 12+8+2, 23 = 12+8+3
However, 23 is not practical because its only proper divisor, 1, cannot be repeated in the sum.
Write a function to determine whether a number is practical.
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