Question

Which summation formula represents the series below?

Answer 1

we are given

$1+2+6+24$

we can rewrite it as

$1+2*1+3*2*1+4*3*2*1$

so, total number of terms is 4

now, we can find nth term

$a_n=n!$

we can write it in sigma form

$\sum _{n=1}^4\:n!$

we can also write it as

$\sum _{n=2}^5\:(n-1)!$

so, option-A.........Answer