The course ends with No. 5 squared.

 No. 5 squared

Way of thinking./ Solution

1. To enter the top 25 before the end of it.
2.  Then put forward a number is multiplied with itself plus 1 => AX (A +1), where A is the next No.5

Example:

  
Note : Is the exponent for the end of the 5 only. 

Techniques, plus a number from 1 to .... anything.

Techniques, plus a number from 1 to .... anything.

Let's see if the problem is what to do.

 1+2+3+4+5+.......+10 = ?

 1+2+3+4+5+.......+21 = ?

The problem and asking if the two will be calculated one by one would take several minutes.

The numbers 1 to 100 is very time consuming.


But we have to think quickly and easily as follows.

From equation (1) M is the last value or maximum value.
And.
The first of. Instead of equation (1) as follows.

Second, the problem is. It can be used in equation (1) as well.


But it may be difficult to calculate. It is strongly recommended to use equation (2) as follows.

The second of. Instead of equation (2) as follows.

Recommendations.

*    If the last number that was used in equation (1).

**  If the last number is odd, use equation (2).

However, the equation (1) and (2) When will the new arrangement.

Which is both even and odd numbers.

This problem is not that difficult anymore.

The magic number 1.

Number one wonders if we multiply a number by the number of digits as well.

The result is as follows.

      1111              or             111111

             x                                         x

      1111                               111111

1234321                    12345654321     Answer

The result is a sequential number. The largest number is equal to the number of No. 1.

From 1, 2, ..... add value to the one by one by one until a maximum number of digits after it is lining up to  

come down one by one and so on. And finally, 2, 1.