a(n) = Sum_{k>=1} floor(n*sqrt(2)^(2-k)).

Terms

a(0) =2a(1) =6a(2) =11a(3) =15a(4) =19a(5) =25a(6) =27a(7) =34a(8) =38a(9) =43a(10) =45a(11) =53a(12) =57a(13) =60a(14) =65a(15) =72a(16) =78a(17) =81a(18) =84a(19) =91a(20) =93a(21) =98a(22) =105a(23) =110a(24) =114a(25) =119a(26) =123a(27) =127a(28) =133a(29) =137