The sequence d[n] defined in A126939.

Terms

a(0) =0a(1) =0a(2) =4a(3) =14a(4) =36a(5) =116a(6) =378a(7) =1178a(8) =3700a(9) =11694a(10) =36852a(11) =116082a(12) =365886a(13) =1153178a(14) =3634154a(15) =11453184a(16) =36095524a(17) =113756584a(18) =358508862a(19) =1129858168a(20) =3560801564a(21) =11222032838a(22) =35366766278a(23) =111460034016a(24) =351271552234