The following questions below the series I and series II shows the same logical patterns

Series I: 218, 227, 238, 252, 270, 293, 320.

Series II: a, b, 342, 356, 374, 397, 426

The correct number in series I is the first number of series II, and the starting logic in series I follow is the same logic in series II. Find the (a + b).