I'm thinking of 8 consecutive positive integers. I arrange them in some order and find the following:
The
number is a multiple of 2.
The
number is a multiple of 3.
The
number is a multiple of 5.
The
number is a multiple of 7.
The
number is a multiple of 11.
The
number is a multiple of 13.
The
number is a multiple of 17.
The
number is a multiple of 19.
Find the smallest possible sum of the 8 consecutive integers I am thinking of.
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If n is the smallest number, then one each of n , n + 1 , n + 2 , n + 3 , n + 4 , n + 5 , n + 6 , n + 7 must be divisible by 2 , 3 , 5 , 7 , 1 1 , 1 3 , 1 7 , 1 9 . Thus, in particular, two of these numbers must be divisible by 1 7 and 1 9 . Solving the appropriate Chinese Remainder Theorem equations, we see that n + a ≡ 0 ( m o d 1 7 ) , n + b ≡ 0 ( m o d 1 9 ) ⇔ n ≡ 1 5 2 a − 1 5 3 b ( m o d 1 7 × 1 9 = 3 2 3 ) and so it is only possible for two of these numbers to be divisible by 1 7 and 1 9 if n is congruent to one of the numbers 1 2 3 3 1 2 9 1 4 9 1 6 8 2 0 2 2 8 4 1 3 3 4 1 3 0 1 5 0 1 6 9 2 0 3 2 8 5 1 4 5 0 1 3 1 1 5 1 1 7 0 2 0 4 2 9 9 1 5 5 1 1 3 2 1 5 2 1 8 3 2 2 1 3 0 0 1 6 9 5 1 3 3 1 6 4 1 8 4 2 6 5 3 0 1 1 7 1 1 2 1 4 6 1 6 5 1 8 5 2 6 6 3 0 2 3 1 1 1 3 1 4 7 1 6 6 1 8 6 2 8 2 3 0 3 3 2 1 1 4 1 4 8 1 6 7 1 8 7 2 8 3 3 0 4 modulo 3 2 3 . It is easy to set up an Excel spreadsheet to test these options, and the smallest value of n for which we get the desired divisibility for all eight numbers is n = 3 3 8 (the second instance of n ≡ 1 5 ( m o d 3 2 3 ) ). This makes the answer 2 7 3 2 .