Bending a piece of wire of length n+1; walks of length n+1 on a tetrahedron; also non-branched catafusenes with n+2 condensed hexagons.

A001998

Bending a piece of wire of length n+1; walks of length n+1 on a tetrahedron; also non-branched catafusenes with n+2 condensed hexagons.

Terms

    a(0) =1a(1) =2a(2) =4a(3) =10a(4) =25a(5) =70a(6) =196a(7) =574a(8) =1681a(9) =5002a(10) =14884a(11) =44530a(12) =133225a(13) =399310a(14) =1196836a(15) =3589414a(16) =10764961a(17) =32291602a(18) =96864964a(19) =290585050a(20) =871725625a(21) =2615147350a(22) =7845353476a(23) =23535971854a(24) =70607649841a(25) =211822683802a(26) =635467254244

External references