The short answer — exact numbers and how we calculated
Royal flush in the five cards available on the flop: 4 / 2,598,960 = 0.000154% — 1 in 649,740.
Holding two fixed Broadway cards of the same suit (A♠K♠) and needing the flop to bring exactly the three missing royal cards: 1 / C(50,3) = 1 in 19,600 ≈ 0.00510%.
Full house in the five cards available on the flop: 3,744 / 2,598,960 = 0.1441% — about 1 in 694.
How we calculated. Each figure counts the five-card combinations that make the hand and divides by all C(52,5) = 2,598,960 five-card combinations of a standard 52-card deck. On the flop a player has exactly five cards available (2 hole + 3 board). The chart further down uses the seven-card distribution instead (2 hole + 5 board by the river), which is why its percentages are higher — the same hand has more five-card combinations to be made from.
Figures verified on 15 September 2026 by direct combinatorial calculation.