a(1)=1. a(n) = Sum_{1<=k<n, gcd(k,n(n+1))=1} a(k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =1a(5) =2a(6) =3a(7) =5a(8) =4a(9) =9a(10) =5a(11) =10a(12) =12a(13) =18a(14) =21a(15) =48a(16) =22a(17) =44a(18) =48a(19) =88a(20) =84a(21) =197a(22) =92a(23) =183a(24) =260a(25) =432a(26) =441a(27) =908a(28) =183a(29) =366