Project Euler 7: The 10001st Prime Number

This mission can be solved by calculating lots of prime numbers. However, we do not want to put extra effort into our solutions, do we? After a bit of searching, I found a list of the 100000 first prime numbers (100008, actually). I saved this file. Unfortunately, it is not in an optimal format. I wrote a short Perl script that creates a new file, in which each prime number is on a separate line:

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# read the file from utm.edu
open( PRIMES, '<', 'dat/100000.txt' ) or die $!;
# this is the file that we will write to
open( TO, '>', 'dat/primes-100000-first.txt' ) or die $!;
while ( <PRIMES> ) { # for each line
        for ( split / +/ ) { # split, separating by spaces, and for each piece
                if ( m/^\d+$/ ) { # if it is a number
                        print TO "$_\n"; # print the number to the file
                }
        }
}
close( TO );
close( PRIMES );

Of course, you need to replace the filenames.

Now, it is a piece of cake to find the 10001st prime number. Just do:

head -10001 dat/primes-100000-first.txt | tail -1

Which finds the 10001 first primes and outputs the last one of them.

Or you could open it in notepad and start counting rows.

Maybe Related?

• Project Euler 10: Sum of First Primes
• Project Euler 3: Find the Largest Prime Factor
• Project Euler 1: Sum of the Multiples of 3 and 5
• Project Euler 8: Greatest Product of Consecutive Digits in String
• Project Euler 4: Largest Palindromic Number with 6 Figures