a(n) = 3 A113405(n)- A113405(n+1).

Terms

a(0) =0a(1) =0a(2) =-1a(3) =1a(4) =2a(5) =5a(6) =7a(7) =14a(8) =27a(9) =57a(10) =114a(11) =229a(12) =455a(13) =910a(14) =1819a(15) =3641a(16) =7282a(17) =14565a(18) =29127a(19) =58254a(20) =116507a(21) =233017a(22) =466034a(23) =932069a(24) =1864135a(25) =3728270a(26) =7456539a(27) =14913081a(28) =29826162a(29) =59652325