Find the largest positive integer n, such that can be expressed as the product of consecutive integers.
Let a positive integer be
Find
x is the remainder when n is divided by 409457 (409457=71x73x79).
The answer is the remainder when x is divided by 1927. (1927=41*47)
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Lemma: the largest integer n that can be represented by ( n − k ) ! consecutive integers is n = ( k + 1 ) ! − 1 .
I don't know a good way to explain this (or just the fact that I'm horrible at explaining things) but here it goes.
Imagine the first k numbers of ( n ) ! they are 2 ⋅ 3 ⋅ 4 . . . . k
Now, We want to add another number to this while still minimizing k (explained later)
The first k+1 numbers become 1 ⋅ 2 ⋅ 3 ⋅ 4 . . . k
Now, think of n! And ( n + 1 ) ! all their numbers overlap except for n+1. So ( n + 1 ) ! has one more number than n!
Now, remove the first k+1 digits (since we're adding one more number (this number is n+1)) and we get n ! = ( k + 1 ) ! ( n + 1 ) n ! . (This is why we want to minimize k+1)
This implies ( k + 1 ) ! − 1 = n
Now, for the rest of our solution
Here, n = ( 2 1 1 + 1 ) ! − 1
It's obvious that 2 1 1 is greater than 79. Thus ( 2 1 1 + 1 ) contains 79,73,71 in it prime factors and is thus is ≡ 0 ( m o d 7 9 , 7 3 , 7 1 )
Since we are subtracting one, it will be ≡ − 1 ( m o d 4 0 9 4 5 7 )
Or ≡ 4 0 9 4 5 6 ( m o d 4 0 9 4 5 7 )
By some calculations 4 0 9 4 5 6 ≡ 9 3 2 ( m o d 1 9 2 7 )