Choose a 2-digit number, say 23, your “seed”.
Form a new 2-digit number: the 10’s digit plus 6 times the units digit.
The example sequence is 23 –> 20 –> 02 –> 12 –> 13 –> 19 –> 55 –> 35 –> …
and its period is the order of the multiplier, 6, in the group of residues relatively prime to the modulus, 10. (59 in this case).
The “random digits” are the units digits of the 2-digit numbers, ie, 3,0,2,2,3,9,5,… the sequence mod 10.

— George Marsaglia via Hillel Wayne