Erroneous version of A002540.

Terms

a(0) =1a(1) =2a(2) =5a(3) =13a(4) =19a(5) =32a(6) =53a(7) =89a(8) =139a(9) =199a(10) =293a(11) =887a(12) =1129a(13) =1331a(14) =5591a(15) =8467a(16) =9551a(17) =15683a(18) =19609a(19) =31397a(20) =155921a(21) =360653a(22) =370261a(23) =492113a(24) =1349533a(25) =1357201a(26) =2010733a(27) =4652353