a(n) = L(2*n+1)+4*n+2.

Terms

a(0) =3a(1) =10a(2) =21a(3) =43a(4) =94a(5) =221a(6) =547a(7) =1394a(8) =3605a(9) =9387a(10) =24518a(11) =64125a(12) =167811a(13) =439258a(14) =1149909a(15) =3010411a(16) =7881262a(17) =20633309a(18) =54018595a(19) =141422402a(20) =370248533a(21) =969323115a(22) =2537720726a(23) =6643838973a(24) =17393796099a(25) =45537549226a(26) =119218851477a(27) =312119005099a(28) =817138163710