The given sequence can be written as: 5 × 2 - 3 = 7 18 × 3 - 3 = 51 69 × 5 - 5 = 342 2, 3 are the prime numbers. So we can say that next number N will be N = 69 × 5 - 3 = 342 Note: Next number is multiple of last number and prime number minus 3. So the answer is N = 342.