Not 1, not 2, not 3, not 4, but 5!

How many nonnegative integers n < 2014 n < 2014 are there such that there will be no possible ordered quintuples of nonnegative integers (not necessarily distinct) ( a , b , c , d , e ) (a, b, c, d, e) that will satisfy the equation a 12 + b 10 + c 8 + d 6 + e 4 = 2 n 1 a^{12} + b^{10} + c^8 + d^6 + e^4 = 2^n - 1


The answer is 2011.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Rindell Mabunga
Sep 19, 2014

We can use modulo 8 8 to solve this problem.

In modulo 8 8 , if x x is an even number, x 12 = x 10 = x 8 = x 6 = x 4 = 0 ( m o d 8 ) x^{12} = x^{10} = x^8 = x^6 = x^4 = 0(mod 8) .

In the other hand if x x is an odd number, x 12 = x 10 = x 8 = x 6 = x 4 = 1 ( m o d 8 ) x^{12} = x^{10} = x^8 = x^6 = x^4 = 1(mod 8) .

When n > 2 n > 2 , 2 n = 0 ( m o d 8 ) 2^n = 0(mod 8) and 2 n 1 = 1 ( m o d 8 ) = 7 ( m o d 8 ) 2^n - 1 = -1(mod 8) = 7(mod 8)

Using these facts we can now solve the problem.

In modulo 8 8 , a 12 + b 10 + c 8 + d 6 + e 4 a^{12} + b^{10} + c^8 + d^6 + e^4 can only be equal to 0 0 , 1 1 , 2 2 , 3 3 , 4 4 , and 5 ( m o d 8 ) 5(mod 8) .

Since 2 n 1 = 7 ( m o d 8 ) 2^n - 1 = 7(mod 8) , n n cannot be greater than 2 2 .

If n n is equal to 0 0 , 1 1 , or 2 2 , there will be ordered quintuples ( a , b , c , d , e ) (a, b, c, d, e) that will satisfy the equation.

Example: If n = 0 n = 0 , ( a , b , c , d , e ) = ( 0 , 0 , 0 , 0 , 0 ) (a, b, c, d, e) = (0, 0, 0, 0, 0)

If n = 1 n = 1 , ( a , b , c , d , e ) = ( 0 , 0 , 0 , 0 , 1 ) (a, b, c, d, e) = (0, 0, 0, 0, 1)

If n = 2 n = 2 , ( a , b , c , d , e ) = ( 0 , 0 , 1 , 1 , 1 ) (a, b, c, d, e) = (0, 0, 1, 1, 1)

Therefore, n = 0 , 1 , 2 n = 0, 1, 2 are the only possible values of n n .

Since there are 2014 2014 nonnegative integers less than 2014 2014 and 3 3 of them are the only possible values of n n . Therefore there are 2014 3 = 2011 2014 - 3 = \boxed{2011} nonnegative integer values of n n such that there will be no possible ordered quintuples of nonnegative integers ( a , b , c , d , e ) (a, b, c, d, e) that will satisfy the equation.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...