Given on day-1, there are 2 organisms. On day- 2 , there are 2*2+3=7 and on day -3 , there are 2*7+3=17.. Let us try to form a pattern: 2=2+0(n=1) 7=4+3(n=2) 17=8+9[8+3⋆3](n=3) 37=16+21[16+3⋆7]n=4 T(n)=2n+3(2n−1−1) We know that 220=210×210=1024×1024, which is more than 1 million. Let us check for n=19
219+3(218−1)=219+3⋅218−3=2⋅219+218−3=220+218−3
which is more than 1 million. Let us check for n=18