For the geometric sequence with a1=4 and r=5 find a5

An infinite geometric series is the sum of an infinite geometric sequence. This series would have no last term. The general form of the infinite geometric series is a1 + a1 r + a1 r2 + a1 r3 + ... a1 + a1 r + a1 r2 + a1 r3 + ..., where a1 a1 is the first term and rr is the common ratio.