Question
What are the missing numbers?
2571, 2621, (a)         , 2721, (b)         , 2821
2 m
(a)

Click button first when a symbol is required. X

(b)

Click button first when a symbol is required. X

What are the missing numbers?
2571, 2621, (a)         , 2721, (b)         , 2821