we are given
[tex] 1+2+6+24 [/tex]
we can rewrite it as
[tex] 1+2*1+3*2*1+4*3*2*1 [/tex]
so, total number of terms is 4
now, we can find nth term
[tex] a_n=n! [/tex]
we can write it in sigma form
[tex] \sum _{n=1}^4\:n! [/tex]
we can also write it as
[tex] \sum _{n=2}^5\:(n-1)! [/tex]
so, option-A.........Answer
