G.f.: Sum_{n=-oo..+oo} x^n * (sqrt(2) + x^n)^(2*n).

Terms

a(0) =1a(1) =3a(2) =4a(3) =15a(4) =16a(5) =52a(6) =77a(7) =184a(8) =256a(9) =716a(10) =1045a(11) =2400a(12) =4320a(13) =9024a(14) =16524a(15) =35439a(16) =65536a(17) =135424a(18) =264928a(19) =534016a(20) =1048856a(21) =2124523a(22) =4196944a(23) =8435712a(24) =16792576a(25) =33658512a(26) =67118016a(27) =134478584a(28) =268435513a(29) =537346048