How can I generate numbers in patterns such as 1,2,1,2,3,4,3,4,5,6,5,6,7,8,7,8... in Excel?

How can I generate numbers in patterns such as 1,2,1,2,3,4,3,4,5,6,5,6,7,8,7,8... in Excel?

Thank you for your help in advance!