Gandhiji Four Monkeys

Gandhi has four monkeys $m_1,m_2,m3_,m_4$. Each of them are having initial supernatural ability $a_1=1,a_2=2,a_3=3,a_4=4$ respectively, to influence people. Total number of people influenced by them in a day is given by $a_1 \times a_2 \times a_3 \times a_4 $. After each day their respective abilities increases by 1. The total number of people influenced till $k^{th}$ day is given as the total