Let be a positive multiple of 7, that leaves a remainder of 1 when divided by 2, 3, 4, 5 or 6.
Fortunately, there are infinite values of .
Find the sum of the least 10 values of .
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The LCM of 2,3,4,5,6 is 60. Thus we want to find integers N such that N ≡ 0 ( m o d 7 ) while N ≡ 1 ( m o d 6 0 ) . Thus N = 7 a = 6 0 b + 1 , so that 7 a − 6 0 b 7 ( a + 1 7 ) = 1 = 2 × 6 0 − 1 7 × 7 = 6 0 ( b + 2 ) so that a + 1 7 = 6 0 c and b + 2 = 7 c for some integer c , and hence we deduce that N = 4 2 0 c − 1 1 9 c ∈ Z The sum of the 10 smallest positive such integers is c = 1 ∑ 1 0 ( 4 2 0 c − 1 1 9 ) = 2 1 9 1 0