a(n) = A047766(6n+2).

Terms

a(0) =0a(1) =0a(2) =1a(3) =5a(4) =26a(5) =133a(6) =708a(7) =3861a(8) =21604a(9) =123266a(10) =715221a(11) =4206956a(12) =25032840a(13) =150413348a(14) =911379384a(15) =5562367173a(16) =34164355848a(17) =211015212580