15 lines
751 B
Markdown
15 lines
751 B
Markdown
|
Starting with 1 and spiralling anticlockwise in the following way, a square spiral with side length 7 is formed.
|
||
|
|
|
||
|
|
~~~
|
||
|
|
37 36 35 34 33 32 31
|
||
|
|
38 17 16 15 14 13 30
|
||
|
|
39 18 05 04 03 12 29
|
||
|
|
40 19 06 01 02 11 28
|
||
|
|
41 20 07 08 09 10 27
|
||
|
|
42 21 22 23 24 25 26
|
||
|
|
43 44 45 46 47 48 49
|
||
|
|
~~~
|
||
|
|
|
||
|
|
It is interesting to note that the odd squares lie along the bottom right diagonal, but what is more interesting is that 8 out of the 13 numbers lying along both diagonals are prime; that is, a ratio of `8/13 = 62%`.
|
||
|
|
|
||
|
|
If one complete new layer is wrapped around the spiral above, a square spiral with side length 9 will be formed. If this process is continued, what is the side length of the square spiral for which the ratio of primes along both diagonals first falls below `10%`?
|