The sequence d[n] defined in A126940.

Terms

a(0) =0a(1) =0a(2) =4a(3) =12a(4) =34a(5) =110a(6) =354a(7) =1120a(8) =3552a(9) =11290a(10) =35862a(11) =113884a(12) =361702a(13) =1148810a(14) =3648670a(15) =11588338a(16) =36805222a(17) =116895404a(18) =371266018a(19) =1179160836a(20) =3745078428a(21) =11894570660a(22) =37777796510a(23) =119984315496a(24) =381076645196