how to find missing numbers in two columns using sql server?

Question

how to find missing numbers in two columns using sql server ?

 

Example

 

Colmn1                       Colmn2

1                                        20

22                                       30

35                                       40

41                                         60

 

 From above solution the no

 

21, 31,32,33,34  are missing from sequence.......

 

Please help me to solve this query......!