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Please answer the question number 14 with proper steps

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Profile image of Ashutosh Rath
7 Years agoGrade 11
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1 Answer

Profile image of Aditya Gupta
7 Years ago
nth term is an=(n^2 – n+1)*(n – 1)!
now if we let f(n)= n*n! then 
an= f(n) – f(n-1) 
this sum telescopes to give
Sn= f(n) – f(0) = n*n! – 0= n*n!
but n*n!= 4000*4000!
so n= 4000