a1=RANDBETWEEN(1,3)
a2=IF(A1=1,RANDBETWEEN(2,3),IF(A1=3,RANDBETWEEN(1,2),CHOOSE(RANDBETWEEN(1,2),1,3)))
a3=6-SUM(A1:A2)

the formula above will create random numbers between 1 and 3 but the numbers will not repeat. I would like to increase the numbers into 7 random numbers (from 1 to 7) but no repeating. Please help. Thank you.

example:
a1 = 3
a2 = 1
a3 = 5
a4 = 2
a5 = 4
a6 = 7
a7 = 6

if I click on refresh, numbers will change randomly but not repeating.