Castell-fact algorithm: RSA, PGP, Bitcoin & Co. 25 partial considerations, using only multiplication and division to break down a composite product into its prime factors. Consideration 19.

Turning away from the attempts (shown in essays 13 to 18 inclusive) to want to factor a large number from left to right. Here continuation of the first 13 essays (initial consideration up to and including consideration 12), each large integer only to be processed FROM RIGHT TO LEFT.