AMC 10 Step by Step
2005 AMC 10BProblem 22P21-25~6 minPrint

For how many positive integers nn less than or equal to 2424 is n!n! evenly divisible by 1+2++n?1 + 2 + \cdots + n?

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Problem © Mathematical Association of America (MAA), American Mathematics Competitions. Reproduced for non-commercial educational use. Solution and commentary are original to this site.