A natural number, it plus L is a multiple of 2, its two times plus 1 is a multiple of 3, its three times plus 1 is a multiple of 5______ .

A natural number, it plus L is a multiple of 2, its two times plus 1 is a multiple of 3, its three times plus 1 is a multiple of 5______ .


Let this natural number be x, then x + 1 = 2K, 2x + 1 = 3M, 3x + 1 = 5N. From the above formula, we can see that x is an odd number. If n = 2, x = 3, then 2 × 3 + 1 is a multiple of 3, so it is not suitable. If n = 5, x = 8, 8 are even numbers, so n = 8, x = 13, 13 × 2 + 1 = 27 is a multiple of 3, and 13 + 1 = 14 is a multiple of 2



There are natural numbers like this: 1 is a multiple of 2, 2 is a multiple of 3, 3 is a multiple of 4, 4 is a multiple of 5, 5 is a multiple of 6, and 6 is a multiple of 7. In this kind of natural number, the smallest number is 1______ .


4 = 2 × 2, 6 = 2 × 3, so the least common multiple of 2, 3, 4, 5, 6, 7 is: 2 × 6 × 5 × 7 = 420420 + 1 = 421; so this number is 421. So the answer is: 421



The sum of a natural number and 3 is a multiple of 5, and the difference between a natural number and 3 is a multiple of 6______ .


Let X be x, then x − 3 = 6nx + 3 = 5Z, N and Z are natural numbers, | x = 6N + 3 and x = 5z-3, | 5Z = 6 (n + 1), when n = 1, 5Z = 12, z = 125 is not the problem; when n = 2, 5Z = 18, z = 185 is not the problem; when n = 3, 5Z = 24, z = 245 is not the problem; when n = 4, 5Z = 30, z = 6 is the problem. So x = 4 × 6 + 3 = 27. So the answer is: 27