Question

I need to generate unique non-sequential alphanumeric string of exactly length 6 (not less, not more).
With non-sequential I mean it should look visually random at first sight and not coming from a sequence (it doesn’t matter if you can find the sequence after some number of days of study, it should just appear random at first sight).
And bear in mind it must be unique.
It’s also unfeasible to lookup all the numbers that have been used already.

I was thinking of letting a database generate a unique number and then apply some function to convert that number into a unique non-sequential alphanumeric string of exactly length 6. Similar to how a hashing algorithm works, but then without possible collisions.

I’ve found this: http://blog.maxant.co.uk/pebble/2010/02/02/1265138340000.html
But the sequence is not visually random.

Answer 1

Is it possible for you to register the generated String sequence to some database/file/someplace? Then one way to do can be for each position (from 1 to 6), randomly pick a character and form your 6 character string. And see if it is one of the registered sequence or not. If already registered, then generated another sequence. If not registered then register & use the generated one for your purpose.