G.f.: exp( Sum_{n>=1} A068963(n)*x^n/n ) where A068963(n) = Sum_{d|n} phi(d^3).

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =20a(5) =52a(6) =105a(7) =253a(8) =536a(9) =1142a(10) =2421a(11) =4999a(12) =10278a(13) =20686a(14) =41512a(15) =81984a(16) =161029a(17) =312681a(18) =603070a(19) =1153284a(20) =2189331a(21) =4129537a(22) =7733317a(23) =14399693a(24) =26644337a(25) =49034811a(26) =89741600a(27) =163411148a(28) =296074694a(29) =533909026