DAY 21

Comment

652 is even, so 2 is a factor, so 2 x ? = 652.

Answer

326.

Readers' methods

Johan de R, Ridderkerk, Netherlands:
Each number n has x of factors. In case n is a square number, x is odd, else x is even. Each pair of divisors other than the square root is placed around the other numbers, such that the numbers are in ascending order.
So the pattern is like this: A1 B1 C1 (D) C2 B2 A2, in which A1 = 1 and A2 = n.
Because the highest factor is n (or A2), the lowest factor is 1 (or A1). Because A2 is even, B1 = 2, so B2 = n/2.

Grace O, York YO19:
To find the next largest number you divide 652 by 2.

Jake A, London SW14:
The largest factor of 652 is 652 .
This is equivalent to dividing by one,
then for the next possible factor divide by two (then 3 then 4....) so it is 652/2 = 326.

L Venters, Auchterarder, PH3:
Answer 326, method is divide by 2.