it's much easier and equally as fast to just learn to square the number rather than learning like 10 different tricks with no apparent pattern between them that each only work on a subset of the numbers and if you really want a formula that breaks down the numbers to make the calculations involved simpler, mn² (where m,n are digits 0-9) = 100m² + 20mn + n² works on all numbers 0-99
The pattern for 50s works with the 60s, except that 11 < n < 19. You will need those squares to do it, though.
it's much easier and equally as fast to just learn to square the number rather than learning like 10 different tricks with no apparent pattern between them that each only work on a subset of the numbers
and if you really want a formula that breaks down the numbers to make the calculations involved simpler, mn² (where m,n are digits 0-9) = 100m² + 20mn + n² works on all numbers 0-99