To write this out algebraically, we can assign variables to the two numbers.
First number = x, Second number = y
The product of the two numbers is x*y or just xy
The sum of the two numbers is (x+y)
The sum of the product and the sum of two positive integers can be expressed as:
xy + x + y, and this is equal to 454, xy + x + y = 454
We can solve for all values of x and y, we get:
xy + x + y = 454
We add 1 to both sides so we can factor:
xy + x + y + 1 = 455
Then we can factor:
x(y+1)+y+1 = 455
(y+1)(x+1) = 455 = 5 * 7 * 13
Their product is the largest only when x = 90 and y = 4
(90*4)(90+4)=33840
Other pairs is not as big, for example, when x = 12 and y = 34
(34*12)(34+12)=18768
To answer your question, the largest possible value is 33840,
I hope this helped,
Gavin