a(n) = a(n-1)*2 + floor(sqrt(a(n-2))).

Terms

a(0) =0a(1) =1a(2) =2a(3) =5a(4) =11a(5) =24a(6) =51a(7) =106a(8) =219a(9) =448a(10) =910a(11) =1841a(12) =3712a(13) =7466a(14) =14992a(15) =30070a(16) =60262a(17) =120697a(18) =241639a(19) =483625a(20) =967741a(21) =1936177a(22) =3873337a(23) =7748065a(24) =15498098a(25) =30998979a(26) =62001894a(27) =124009355a(28) =248026584a(29) =496064303