The sequence a[n]+b[n]+c[n]+d[n] defined in A126939.

Terms

a(0) =1a(1) =5a(2) =15a(3) =47a(4) =149a(5) =469a(6) =1477a(7) =4657a(8) =14677a(9) =46251a(10) =145765a(11) =459391a(12) =1447783a(13) =4562753a(14) =14379751a(15) =45318455a(16) =142823219a(17) =450114149a(18) =1418555997a(19) =4470646047a(20) =14089451907a(21) =44403572399a(22) =139939952691a(23) =441027361411