a(1) = 1; a(n) = a(n-1) + sigma(a(n-1)) where sigma(k) = sum of the divisors of k.

Terms

a(0) =1a(1) =2a(2) =5a(3) =11a(4) =23a(5) =47a(6) =95a(7) =215a(8) =479a(9) =959a(10) =2063a(11) =4127a(12) =8255a(13) =19007a(14) =38327a(15) =76655a(16) =168647a(17) =338663a(18) =708263a(19) =1453823a(20) =3308543a(21) =7154303a(22) =14919599a(23) =29910119a(24) =59820239a(25) =119676959a(26) =239387375a(27) =538142975a(28) =1205440295a(29) =2651968655