The mystical elements and interconnected symbols in Riddley Walker are intimately connected with numbers—or, as Riddley always abbreviates and capitalizes, Nos.
One and two: The 1 Big 1 is both the ultimate secret sought by Eusa and the source of ultimate destruction; the 1 Littl 1 is its counterpart on a more human scale. Duality and division are recurring themes, especially in the Eusa story where Eusa's two dogs lead him to the Littl Shyning Man, who is then torn in half ("Lukin for the 1 yu wil aul ways fyn thay 2 ... Thay 2 is 2ce as bad as the 1"). The Big 2 are the heads of state.
Four: Eusa's original family, reunited in death; Salt 4; the four classical elements.