Coefficients arising in the enumeration of configurations of linear chains.

Terms

a(0) =0a(1) =0a(2) =1a(3) =4a(4) =11a(5) =32a(6) =92a(7) =254a(8) =672a(9) =1778a(10) =4622a(11) =11938a(12) =30442a(13) =77396a(14) =194896a(15) =489620a(16) =1221134a(17) =3040194a(18) =7524933a(19) =18600478a(20) =45756483a(21) =112444948a(22) =275204606a(23) =673031750a(24) =1640168584a(25) =3994716336a(26) =9699476314