+0  
 
0
300
2
avatar

Is the following number Prime or Composite?   9999997777 7755555533 3333111111 . Notice the descending order of the odd numbers grouped in strings of fives!. Thanks for any help.

Guest Apr 15, 2017
 #1
avatar
+1

Very interesting and clever, whoever came up with it!!.

However, using a primality test shows that it is a composite number and factors as follows:

999999 777777 555555 333333 111111 = 3 x 7 x 11 x 13 x 37 x 9000007000005000003000001.

 

P.S. Notice that it is grouped in "sixes" not "fives". Also, notice that all its factors are odd!.

Guest Apr 15, 2017
 #2
avatar+26971 
+1

Calculate the digital root:  

6*(9+7+5+3+1) = 150

1+5+0 = 6  

6 is divisible by 3 hence the original number is divisible by 3, so it is composite, not prime.

.  

Alan  Apr 16, 2017

29 Online Users

avatar

New Privacy Policy

We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive information about your use of our website.
For more information: our cookie policy and privacy policy.