Why are the last two lines put within brackets?

In each of the following number series. two number have been put within brackets.mark your anser as (2), 5, (12), 25, 41, 61

In the following number series, two numbers have been put within brackets. Select the most appropriate option for these numbers in relation to their inclusion in the series. 2, 4, 6, 8, 10, (12), 14, 16, (18), 20

In the following number series, two numbers have been put within brackets. Select the most appropriate option for these numbers in relation to their inclusion in the series. 21, 24, 19, (29), 17, 28, (15), 30

In the following number series, two numbers have been put within brackets. Select the most appropriate option for these numbers in relation to their inclusion in the series. 1, 9, 25, 49, (81), 121, 169, (215), 289

In the following number series, two numbers have been put within brackets. Select the most appropriate option for these numbers in relation to their inclusion in the series. 0, 7, 26, (65), 124, 215, (344), 511

In the following number series, two numbers have been put within brackets. Select the most appropriate option for these numbers in relation to their inclusion in the series. 1, 5, 17, (39), 65, 101, (145), 197

In the following number series, two numbers have been put within brackets. Study the series carefully andselect the correct alternative with respect to the series. 0, 7, 26, 63, (124), 215, 342, (512)