Quad
Slot-machine-grade uniformity.
The digit string contains four identical adjacent digits, like 11112, 788880 or 999999. Runs of five or six are included.
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Only 2,701 exist, about 0.27% — 13 times rarer than the Triple. Demanding one more matching digit costs an order of magnitude: repetition’s “exponential tax” made visible.
Every quad is automatically a triple, so both features always fire together and are paid separately under the group weighting. The six-digit repdigits (111111 and kin, 9 in total) are the quad’s final form, containing three overlapping quads at once.
Four of a kind (7777) is the slot machine’s near-jackpot, and the casino paytable agrees eerily with the site-wide counts: each extra matching digit divides rarity by roughly ten.