Windhoe

Every single day, you generate a fresh 256-digit random pool (giving you 10²⁵⁶ possible values), combine it with that day's visitor count (between 1 and 100,000, adding 10⁵ possibilities) and a millisecond-precision timestamp (another 10⁷ variations per day), then feed that entire string into SHA-512 to produce a perfectly distributed hash; you take that hash, reduce it modulo 10¹² to get a valid starting position within your 1-trillion-digit library of Pi, extract 128 consecutive digits from that position, chop those 128 digits into 8 separate seeds of 16 digits each, multiply all 8 seeds together to get a massive product, add all 8 seeds together to get a sum, XOR those two results together to scramble any mathematical relationship between them, and output that final XOR result as your 128-digit code.

Because the SHA-512 hash ensures that even microscopic changes in the pool, visitor count, or time produce completely different indices, and because your final output has 10¹²⁸ possible values, the Birthday Paradox says you would need to generate roughly the square root of that 10⁶⁴ codes before hitting a 50% chance of repetition, which at one code per day equals 10⁶⁴ days or approximately 10⁶¹ years, meaning this system will take a hundred quintillion trillion trillion trillion trillion times longer than the current age of the universe to produce the same number twice, making repetition effectively impossible for all practical and astronomical timescales.