a(n) = 3*A131666(n) - A131666(n+1).

Terms

a(0) =0a(1) =-1a(2) =2a(3) =1a(4) =3a(5) =2a(6) =7a(7) =13a(8) =30a(9) =57a(10) =115a(11) =226a(12) =455a(13) =909a(14) =1822a(15) =3641a(16) =7283a(17) =14562a(18) =29127a(19) =58253a(20) =116510a(21) =233017a(22) =466035a(23) =932066a(24) =1864135a(25) =3728269a(26) =7456542a(27) =14913081a(28) =29826163a(29) =59652322