Browse · MATH
Printjmc
number theory senior
Problem
What is the least whole number that is divisible by 7, but leaves a remainder of 1 when divided by any integer 2 through 6?
Solution
If leaves a remainder of 1 when divided by 2, 3, 4, 5, and 6, then is divisible by all of those integers. In other words, is a multiple of the least common multiple of 2, 3, 4, 5, and 6. Prime factorizing 2, 3, 4, 5, and 6, we find that their least common multiple is . Thus the possible values for an integer which is one more than a multiple of 2, 3, 4, 5, and 6 are 61, 121, 181, 241, 301 and so on. Checking them one at a time, we find that the least of these integers which is divisible by 7 is .
Final answer
301