Insert the missing number.

3, 7, 6, 5, 9, 3, 12, 1, 15, (....)

The terms are alternatively multiplied by 1.5 and divided by 3. However, 18.5 does not satisfy it.

The differences between two successive terms from the beginning are 7, 5, 7, 5, 7, 5.

So, 40 is wrong.

Alternatively 23 is added and 17 is subtracted from the terms. So, 634 is wrong.

Terms at odd places are 5, 6, 7, 8 etc. and each term at even place is 16.

So, 9 is wrong.

The Sum of the digits in each number, Except 324 is 10.

In each number except 383, the product of first and third digits is the middle one.

Each of the numbers except 28, is a multiple of 3.

Let the given numbers be A, B, C, D, E, F, G.

Then, A, A x 1 + 1, B x 2 + 2, C x 3 + 3, D x 4 + 4, E x 5 + 5, F x 6 + 6 are the required numbers.

Clearly, 228 is wrong.