Apply partial sum operator twice to Stern's sequence.

Terms

a(0) =1a(1) =3a(2) =7a(3) =14a(4) =27a(5) =51a(6) =95a(7) =179a(8) =340a(9) =649a(10) =1243a(11) =2407a(12) =4691a(13) =9175a(14) =17982a(15) =35287a(16) =69588a(17) =137596a(18) =272448a(19) =539868a(20) =1070224a(21) =2122129a(22) =4217132a(23) =8389833a(24) =16700934a(25) =33255128a(26) =66228664a(27) =131908316