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A TASTE OF RAMANUJAN'S MATH

 

      Ramanujan, an expert in number theory.  We will see, one of his works.
          3= 3
          3 = 2+1
          3 = 1+1+1
     Here 3 is written in three ways.  A natural number is expressed as sum of natural numbers.
      4= 4
      4 = 3+1
      4 = 2 + 2
      4 = 2+1+1
      4 = 1+1+1+1
     Here 4 is expressed in 5 different ways.
     We define "partition number" p(n) as the number of ways a given natural number 'n' can be written as a sum of natural numbers.
     Hence p(3)=3
                 p(4)=5
     It seems easy to find out the partition number.  But as the number gets larger, everything goes out of hand.  Partition number for 1 to 10 is given below.

n    p(n)        n     p(n)

1     1           6       11
2     2            7       15
3     3            8       22
4     5           9        30
5     7          10       42

   p(n) goes on increasing exponentially.  Is there a procedure or a formula to find the partition number of 'n'?  Ramanujan gave 'almost a correct formula' to calculate p(n).
That is

p(n) = 1/[4 pi root of 3] *eˆ[pi root of 2n/3]

     The accuracy of formula increases as the  n  increases. 
for example
   p(100) = 190569292,

     It is exactly correct.
     Partion number formula eluded mathematicians for centuries.  Ramanujan made a breakthrough.  This formula (paper) is mainly responsible for his election as a follow of the Royals society.   
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