Number of Schur rings over Z_{2^n}.

Terms

a(0) =1a(1) =1a(2) =3a(3) =10a(4) =37a(5) =151a(6) =657a(7) =2989a(8) =14044a(9) =67626a(10) =332061a(11) =1656893a(12) =8379773a(13) =42871890a(14) =221528317a(15) =1154624725a(16) =6063752579a(17) =32058277129a(18) =170492969062a(19) =911505351447