Duplicate of A002714.

Terms

a(0) =1a(1) =7a(2) =19a(3) =53a(4) =149a(5) =421a(6) =1193a(7) =3387a(8) =9627a(9) =27383a(10) =77923a(11) =221805a(12) =631469a(13) =1797957a(14) =5119593a(15) =14578387a(16) =41514003a(17) =118218823a(18) =336653331a(19) =958698053a(20) =2730124261a(21) =7774706437a(22) =22140438345a(23) =63050541515a(24) =179552587883a(25) =511322221559