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 #1
avatar+2448 
+1
Dec 17, 2018
 #6
avatar+26367 
+9

the positive integers are arranged in the pattern illustrated below if this pattern continues indefinitely, what is the number immediately above 39863?

1  2 5 10 17 26

3  4 7 12 19 28

6  8 9 14 21 30

11 13 15 16 23 32

18 20 22 24 25 34

27 29 31 33 35 36

 

Source: https://www.algebra.com/algebra/homework/word/misc/Miscellaneous_Word_Problems.faq.question.1131667.html

 

Let row = n

Let column = k

 

Formula:

\(\begin{array}{|rcll|} \hline T(n,k) &=& (k-1)^2+2n-1 \qquad & n\le k \\ T(n,k)&=&(n-1)^2+2k \qquad & n>k \\ \hline \end{array}\)

Source: http://oeis.org/search?q=a185725&sort=&language=english

 

1. \(\begin{array}{|rcll|} \hline \sqrt{39863} &=& 199.657\ldots \\ n_{min} &=& 199 \\ n_{max} &=& 200 \\ \hline \end{array}\)

 

 

\(\begin{array}{|rcll|} \hline T(200,k) &=& (200-1)^2+2k \qquad & n>k \\ 39863 &=& 199^2+2k \\ 2k &=& 39863 - 199^2 \\ 2k &=& 262 \\ \mathbf{k}& \mathbf{=}& \mathbf{131} \\ \hline \end{array} \)

 

The number immediately above:

\(\begin{array}{|rcll|} \hline T(199,131) &=& (199-1)^2+2\cdot 131 \qquad & n>k \\ T(199,131) &=& 198^2+2\cdot 131 \\ \mathbf{T(199,131)} & \mathbf{=}& \mathbf{39466} \\ \hline \end{array}\)

 

laugh

Dec 17, 2018
 #24
avatar+118608 
0
Dec 17, 2018

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