2013, 2014, 2015, 2016!

Level 2

Let p p be the largest integer n n such that 201 3 n 2013^n divides 2013 ! 2013! . Let q q be the largest integer m m such that 201 4 m 2014^m divides 2014 ! 2014! . Let r r be the largest integer s s such that 201 5 s 2015^s divides 2015 ! 2015! Find the largest integer x x such that [ ( p + 1 ) ( q 2 ) ( r + 3 ) ] x [(p+1)(q-2)(r+3)]^x divides 2016 ! 2016! .


The answer is 124.

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

Brian Moehring
Aug 23, 2018

To solve this, we will use the function N ( m , n ) = largest integer x such that m x divides n ! N(m,n) = \text{ largest integer }\, x\, \text{ such that }\, m^x\, \text{ divides }\, n! which is well-known to have the properties p prime N ( p , n ) = k = 1 n p k N ( m k , n ) = 1 k N ( m , n ) N ( lcm { m 1 , m 2 , , m k } , n ) = min { N ( m 1 , n ) , N ( m 2 , n ) , , N ( m k , n ) } } p \text{ prime} \implies N(p,n) = \sum_{k=1}^\infty \left\lfloor\frac{n}{p^k}\right\rfloor \\ N(m^k,n) = \left\lfloor\frac{1}{k}N(m,n)\right\rfloor \\ N\left(\text{lcm}\{m_1,m_2,\ldots,m_k\},n\right) = \min\left\{N(m_1,n), N(m_2,n), \ldots, N(m_k,n)\right\}\}


Turning toward the problem at hand, p = N ( 2013 , 2013 ) = N ( 3 × 11 × 61 , 2013 ) = min { N ( 3 , 2013 ) , N ( 11 , 2013 ) , N ( 61 , 2013 ) } = N ( 61 , 2013 ) = 33 q = N ( 2014 , 2014 ) = N ( 2 × 19 × 53 , 2014 ) = min { N ( 2 , 2014 ) , N ( 19 , 2014 ) , N ( 53 , 2014 ) } = N ( 53 , 2014 ) = 38 r = N ( 2015 , 2015 ) = N ( 5 × 13 × 31 , 2015 ) = min { N ( 5 , 2015 ) , N ( 13 , 2015 ) , N ( 31 , 2015 ) } = N ( 31 , 2015 ) = 65 + 2 = 67 \begin{aligned} p &= N(2013, 2013) \\ &= N(3\times 11\times 61, 2013) \\ &= \min\left\{N(3,2013), N(11,2013), N(61,2013)\right\} \\ &= N(61,2013) \\ &= 33 \\ { } \\ q &= N(2014, 2014) \\ &= N(2\times 19\times 53, 2014) \\ &= \min\left\{N(2,2014), N(19,2014), N(53,2014)\right\} \\ &= N(53,2014) \\ &= 38 \\ { } \\ r &= N(2015, 2015) \\ &= N(5\times 13\times 31, 2015) \\ &= \min\left\{N(5,2015), N(13,2015), N(31,2015)\right\} \\ &= N(31,2015) \\ &= 65 + 2 \\ &= 67 \end{aligned}

so that N ( ( p + 1 ) ( q 2 ) ( r + 3 ) , 2016 ) = N ( 2 4 × 3 2 × 5 × 7 × 17 , 2016 ) = min { 1 4 N ( 2 , 2016 ) , 1 2 N ( 3 , 2016 ) , N ( 5 , 2016 ) , N ( 7 , 2016 ) , N ( 17 , 2016 ) } = min { 1 4 N ( 2 , 2016 ) , 1 2 N ( 3 , 2016 ) , N ( 17 , 2016 ) } = min { 502 , 502 , 124 } = 124 \begin{aligned} N\Big((p+1)(q-2)(r+3),2016\Big) &= N\Big(2^4\times 3^2\times 5\times 7\times 17,2016\Big) \\ &= \min\left\{\left\lfloor\frac{1}{4}N(2,2016)\right\rfloor, \left\lfloor\frac{1}{2}N(3,2016)\right\rfloor, N(5,2016), N(7,2016), N(17,2016)\right\} \\ &= \min\left\{\left\lfloor\frac{1}{4}N(2,2016)\right\rfloor, \left\lfloor\frac{1}{2}N(3,2016)\right\rfloor, N(17,2016)\right\} \\ &= \min\{502, 502, 124\} \\ &= \boxed{124} \end{aligned}

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...