Third line of 4-wave sequence A038197.

Terms

a(0) =1a(1) =2a(2) =9a(3) =19a(4) =75a(5) =160a(6) =622a(7) =1329a(8) =5157a(9) =11021a(10) =42756a(11) =91376a(12) =354484a(13) =757588a(14) =2938977a(15) =6281058a(16) =24366645a(17) =52075371a(18) =202020427a(19) =431749580a(20) =1674922950a(21) =3579575053a(22) =13886550633a(23) =29677753369a(24) =115131438424a(25) =246054079584a(26) =954538564968