Question

ok find a1 a2 a3 a4 when you have a subscript n = 2(n+3)!

Answer 1

\[a_n=2(n+3)!\]

Answer 2

replace n by 1, 2, 3 just like a function. for example
\[a_1=2(1+3)!\]
\[a_1=2\times 4!\]
\[a_1=2\times 4\times 3\times 2=48\]