f(n, m) = (n + m) × n

e.g. f(2, 3) = (2 + 3) × 2 = 10

Hence, f(9, 7) = (9 + 7) × 9 = 144

To get the next number, multiply the previous number in the series by itself plus one:

n × (n + 1).

For example, to get 6, multiply 2 × (2 + 1)
To get 42 multiply 6 × (6 + 1)

Thus, 1806 × 1807 = 3263442

240. To get the number, multiply the previous number in the series by its position. 48 is in the 5th position, so 48 × 5 = 240

13112221

The next number in the series counts the previous numbers. Thus the first number is 1, which is one 1, or 11. To describe 11, you have two 1’s, or 21. Now you have one 2 and one 1, so the next number is 1211. The solution is to continue describing the previous number using only numbers.

The numbers are in alphabetical order.

8 = eight
5 = five
4 = four
9 = nine
1 = one
7 = seven
6 = six
10 = ten
3 = three
2 = two
0 = zero