a(n) = Sum_{k=1..n} floor((n/k)^k).

Terms

a(0) =1a(1) =3a(2) =6a(3) =11a(4) =18a(5) =31a(6) =48a(7) =76a(8) =118a(9) =184a(10) =279a(11) =426a(12) =641a(13) =966a(14) =1448a(15) =2163a(16) =3228a(17) =4805a(18) =7137a(19) =10586a(20) =15681a(21) =23198a(22) =34278a(23) =50606a(24) =74632a(25) =109987a(26) =161954a(27) =238312a(28) =350432a(29) =514999