a(n) = floor(2^n cot(1/n)).

Terms

a(0) =1a(1) =7a(2) =23a(3) =62a(4) =157a(5) =380a(6) =889a(7) =2037a(8) =4589a(9) =10205a(10) =22465a(11) =49038a(12) =106285a(13) =228985a(14) =490791a(15) =1047210a(16) =2225653a(17) =4713736a(18) =9952272a(19) =20954040a(20) =44006898a(21) =92211129a(22) =192816394a(23) =402420140a(24) =838413359a(25) =1743970009a(26) =3622221495a(27) =7512996836a(28) =15563085028a(29) =32200323371