G.f.: exp( Sum_{n>=1} A174478(n)*x^n/n ) where A174478(n) = Sum_{d|n} d*2^(n/d)*tau(d).

Terms

a(0) =1a(1) =2a(2) =8a(3) =20a(4) =58a(5) =136a(6) =348a(7) =788a(8) =1856a(9) =4094a(10) =9160a(11) =19716a(12) =42692a(13) =90152a(14) =190628a(15) =396800a(16) =825170a(17) =1698432a(18) =3490484a(19) =7124396a(20) =14517896a(21) =29450384a(22) =59654636a(23) =120472948a(24) =243010964a(25) =489208250a(26) =983952448a(27) =1976442696a(28) =3967448276a(29) =7957317632