Exactly One Pair
Almost special — and that’s exactly the point.
Three or more digits, with exactly one digit value appearing twice and all others once: 1123 and 368350 qualify; 1122 (two pairs) and 111 (a triple) do not. “Exactly” is a hard condition.
Your record
There are 457,731 of them — 45.77%, nearly one in two numbers, the widest structural feature on the site. At base 23 EP it is the rightful king of commoners.
That 45.77% isn’t a guess: it has been cross-checked against published probability values. Among six-digit numbers the share is about 48%, slightly under the naive complement of “all distinct” — triples, two-pairs and three-pairs all siphon off probability.
“Exactly” seals both directions: one more repetition (triple, two pairs) and you’re out; no repetition at all (all distinct) and you’re out too. It is the dead center of the rarity spectrum — the floor of the rarity game.