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p+q-pq=154, p,q prime (Slovenia 1997 4th Grade P1)

Source:

May 3, 2021

Diophantine equationnumber theory

Problem Statement

Marko chose two prime numbers

a

and

b

with the same number of digits and wrote them down one after another, thus obtaining a number

c

. When he decreased

c

by the product of

a

and

b

, he got the result

154

. Determine the number

c