Sum of every third term of the Padovan sequence A000931.

Terms

a(0) =1a(1) =2a(2) =3a(3) =5a(4) =10a(5) =22a(6) =50a(7) =115a(8) =266a(9) =617a(10) =1433a(11) =3330a(12) =7740a(13) =17992a(14) =41825a(15) =97230a(16) =226031a(17) =525457a(18) =1221538a(19) =2839730a(20) =6601570a(21) =15346787a(22) =35676950a(23) =82938845a(24) =192809421a(25) =448227522a(26) =1042002568a(27) =2422362080a(28) =5631308625a(29) =13091204282