Self-composition of the number of divisors function (A000005).

Terms

a(0) =1a(1) =4a(2) =12a(3) =34a(4) =92a(5) =246a(6) =640a(7) =1660a(8) =4264a(9) =10914a(10) =27732a(11) =70247a(12) =177466a(13) =447570a(14) =1126344a(15) =2828465a(16) =7089391a(17) =17746456a(18) =44384884a(19) =110927184a(20) =276993616a(21) =691007612a(22) =1722214602a(23) =4289021667a(24) =10675557184a(25) =26561494820a(26) =66063726382a(27) =164248795485a(28) =408168287028