Suppose, you have been given the task to generate a sequence of numbers and repeat them. For example -

1,2,3,4,1,2,3,4,1,2,3,4

You can use the below formula and drag down -

=MOD(ROWS($1:1)-1,4)+1

Replace 4 with with any other number to generate any other sequence. Hence, if you want to generate 1,2,3,4,5,6,7,8,9,10,1,2,3,4,5,6,7,8,9,10,1,2,3,4,5,6,7,8,9,10 then formula becomes -

=MOD(ROWS($1:1)-1,10)+1

The structure of the formula is

=MOD(ROWS($1:1)-1,X)+Y

X - Number of numbers
Y - Starting Number

Utilizing above formula, you want to generate the sequence 5,6,7,8,9,10,5,6,7,8,9,10,5,6,7,8,9,10, then use below formula (You need 6 numbers and stating number is 5)

=MOD(ROWS($1:1)-1,6)+5