The sum of all divisors of this semiprime number is 2696.
What is the number?
Bonus: What if the word "semiprime" was erased from the puzzle?
The number is 2019.
Its factors sum 1+3+673+2019=2696.
Method: let the prime factors be (a,b) then 1+a+b+ab=2696.
b=(2695-a)/(1+a)
Search by table only needs to go (odd primes) from 3 to 51. Only a=3 gives prime b.
Bonus: If you erase "semiprime" the puzzle becomes harder.
Edit: This chart implies there are no other numbers
http://oeis.org/A085790/a085790.txt
Edited on February 13, 2019, 1:47 pm
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Posted by Jer
on 2019-02-13 12:48:24 |
Solution by year.
