a(n) = Product_{d|n, d>1} (d - 1).

Terms

a(0) =1a(1) =1a(2) =2a(3) =3a(4) =4a(5) =10a(6) =6a(7) =21a(8) =16a(9) =36a(10) =10a(11) =330a(12) =12a(13) =78a(14) =112a(15) =315a(16) =16a(17) =1360a(18) =18a(19) =2052a(20) =240a(21) =210a(22) =22a(23) =53130a(24) =96a(25) =300a(26) =416a(27) =6318a(28) =28a(29) =146160