Apply partial sum operator thrice to Stern's sequence.

Terms

a(0) =1a(1) =4a(2) =11a(3) =25a(4) =52a(5) =103a(6) =198a(7) =377a(8) =717a(9) =1366a(10) =2609a(11) =5016a(12) =9707a(13) =18882a(14) =36864a(15) =72151a(16) =141739a(17) =279335a(18) =551783a(19) =1091651a(20) =2161875a(21) =4284004a(22) =8501136a(23) =16890969a(24) =33591903a(25) =66847031a(26) =133075695a(27) =264984011