Let 1 , a 1 , a 2 , … , a k be all the positive divisors of N = 2 7 4 2 0 7 2 8 0 ( 2 7 4 2 0 7 2 8 1 − 1 ) arranged in ascending order. And let T denote the number of ways to express N as the product of two coprime factors.
Compute K + ( i = 1 ∑ K a i 1 ) + T .
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How do you know that p = 2 7 4 2 0 7 2 8 1 − 1 is a prime number?
It is The Largest Known Prime Number Till Date.
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N = 2 n − 1 ( 2 n − 1 ) N = 2 n − 1 ( p ) W h e r e n = 7 4 2 0 7 2 8 1 a n d p = 2 7 4 2 0 7 2 8 1 − 1 i s a P r i m e N u m b e r D i v i s i o r s O f N a r e { 1 , 2 , 2 2 , 2 3 , 2 4 , 2 5 , 2 6 , . . . . . . , 2 n − 1 , p , 2 p , 4 p , 8 p , . . . . . , 2 n − 1 p } N o w k = 2 n − 1 w h i c h i s T o t a l N u m b e r o f D i v i s o r s ∑ i = 1 k a i 1 = 2 1 + 2 2 1 + 2 3 1 + . . . . . 2 n − 1 1 + p 1 ( 2 1 + 2 2 1 + 2 3 1 + . . . . . 2 n − 1 1 ) = 1 + 2 1 + 2 2 1 + 2 3 1 + . . . . . 2 n − 1 1 + p 1 ( 2 1 + 2 2 1 + 2 3 1 + . . . . . 2 n − 1 1 ) − 1 T a k i n g L . C . M . = p 2 n − 1 ( 2 0 + 2 1 + 2 2 + . . . . . 2 n − 1 ) ( p 0 + p 1 ) − 1 = 1 T = 2 r − 1 w h e r e r i s t h e N u m b e r O f P r i m e N u m b e r s H e r e r = 2 T = 2 N o o f w a y s t o e x p r e s s N a s a p r o d u c t o f T w o C o − p r i m e F a c t o r s N o w K + ∑ i = 1 k a i 1 + T = 2 ( n ) − 1 + 1 + 2 = 2 ( 7 4 2 0 7 2 8 1 ) + 2 = 1 4 8 4 1 4 5 6 4