| Title: | Mathematics at DEC | 
| Moderator: | RUSURE::EDP | 
| Created: | Mon Feb 03 1986 | 
| Last Modified: | Fri Jun 06 1997 | 
| Last Successful Update: | Fri Jun 06 1997 | 
| Number of topics: | 2083 | 
| Total number of notes: | 14613 | 
    I need to know the 5th perfect number, the one that comes after
    8128.
    
    kevin
| T.R | Title | User | Personal Name | Date | Lines | 
|---|---|---|---|---|---|
| 633.1 | Easy enough to check it out... | OMEGA::REILLY | Fri Dec 19 1986 18:17 | 6 | |
|     I don't know why, but I seem to remember that it is 33,550,336
    but then again, I may be wrong.....                           
    
    						matt
    (then again, it may have been the combination to a gym locker, 
    the number sticks in my head for some reason....)
 | |||||
| 633.2 | More rigorous method | OMEGA::REILLY | Fri Dec 19 1986 18:55 | 34 | |
|     
For what it is worth....
       	       8128 = 2 ^ 6 * (2 ^ 7 - 1)
       
     Since 2 ^ 7 - 1 is prime, 8128 is perfect.  (This is easily proved 
by someone who is suitably awake.)
     All of the known perfect numbers are of the form 
2 ^ (p - 1) * (2 ^ p - 1)  where p is prime and (2 ^ p - 1)
is prime.
       
isprime(2^11 - 1);
                                     false
isprime(2^13 - 1);
                                      true
evalf(2^12 * (2 ^ 13 - 1));
                                   33550336.
quit;
       	       	       	       	       	       	    matt
btw, for grins try the above commands to MAPLE in a batch job 
without the quit command at the end.... i.e. the following...
$ maple -q
isprime(2^11 - 1);
isprime(2^13 - 1);
evalf(2^12 * (2 ^ 13 - 1));
convert(2^12 * (2 ^ 13 - 1),  binary);
    
 | |||||
| 633.3 | More perfect numbers | MODEL::YARBROUGH | Mon Dec 22 1986 08:26 | 23 | |
| The next few perfect numbers are 2^(k-1) * (2^k-1) for k=17 8589869056 k=19 137438691328 k=31 2305843008139952128 k=61 k=89 k=107 k=127 k=521 k=607 k=1279 k=2203 k=2281 k=3217 k=4253 k=4423 k=9689 k=9941 (5985 digits) The primes of the form 2^k-1 are the corresponding Mersenne primes. The information above is taken from Beiler's *Recreations in the Theory of Numbers*, p19. | |||||