Numbers on a Board
At the beginning of the day, four integers are written on the board (`a_0,b_0,c_0,d_0`). Every minute, Danny replaces the four numbers on the board with a new set of four numbers according to the following rule: If the numbers written on the board are (a,b,c,d), Danny first generates the numbers
`a'=a+4b+16c+64d`
`b'=b+4c+16d+64a`
`c'=c+4d+16a+64b`
`d'=d+4a+16b+64c`
Then he erases the numbers (a,b,c,d) and writes in their place the numbers (a',d',c',b'). For which initial sets (`a_0,b_0,c_0,d_0`) will Danny eventually write a set of four numbers that are all divisible by `5780^5780`
Difficulty level (1 very easy - 10 very hard): 3
Topics:
Number Theory
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Modular Arithmetic / Remainder Arithmetic
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Divisibility Rules
Number Theory
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Division
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Parity (Even/Odd)
Algebra
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Sequences
- Gillis Mathematical Olympiad, 2019-2020 Question 4
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