Question

What number comes next in the series? 31, 1031, 402, 16, ____

Answer 1

There could be many answers for this question. In general, the number that comes after 16 is a number with 8 as the sum of its digits.

Explanation:

1st number 31 – Sum of digits is 3 + 1 = 4  

2nd number 1031 – Sum of digits is 1 + 0 + 3 + 1 = 5

3rd number 402 – Sum of digits is 4 + 0 + 2 = 6

4th number 16 – Sum of digits is 1 + 6 = 7

Therefore, the missing number could be the single digit number 8 or any of the two-digit numbers 17, 26, 35, 44, 53, 62, 71 or 80. It could also be a bigger number with the digits of any of the given two-digit numbers and 0 for the other digits such as 260 or 7001.

Answer 2

The number that comes next in the series could be any number whose digits add up to a total of 8. 

As the previous numbers in the series all are following the rule of increasing counted numbers. For example:
31 counts up to 4
1031 counts up to 5
402 counts up to 6
16 counts 7.

Thus, all the possible numbers could be
single digit: 8 itself 
double digit: 17, 26, 35 ,44, 53, 62, 71, 80
triple digit: 107,305, 323, 422, 512, 620, 800