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posted by john on Wednesday, August 1, 2012 at 9:22pm.
Find the remainder when 1!+2!+...+299!+300! is divided by 21
If you note that we only need to calculate 6 s=∑ i! n=1 or s=873 mod 21 = 12 Because all terms 7! and beyond are divisible by 21.
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