a(1) = 16, a(n) = sigma(a(n-1)).

Terms

a(0) =16a(1) =31a(2) =32a(3) =63a(4) =104a(5) =210a(6) =576a(7) =1651a(8) =1792a(9) =4088a(10) =8880a(11) =28272a(12) =79360a(13) =196416a(14) =633984a(15) =1827840a(16) =7074432a(17) =22032000a(18) =86640840a(19) =364989240a(20) =1651141800a(21) =7540142400a(22) =33541980160a(23) =90193969152a(24) =334471118520