7, 8, 18, 57, ?, 1165, 6996

Here 2nd number = (1st number x 1 )+1

 3rd number = (2nd number x 2 +2) 

4th number = (3rd number x 3 )+3 and so on..

Therefore, 5th number = (4th number x 4) +4 =57 x 4 + 4 =232.