Number of 2-matchings of the n X n grid graph.

Terms

a(0) =2a(1) =44a(2) =224a(3) =686a(4) =1622a(5) =3272a(6) =5924a(7) =9914a(8) =15626a(9) =23492a(10) =33992a(11) =47654a(12) =65054a(13) =86816a(14) =113612a(15) =146162a(16) =185234a(17) =231644a(18) =286256a(19) =349982a(20) =423782a(21) =508664a(22) =605684a(23) =715946a(24) =840602a(25) =980852a(26) =1137944a(27) =1313174a(28) =1507886a(29) =1723472