Column k=2 of triangle A257673.

Terms

a(0) =1a(1) =6a(2) =21a(3) =62a(4) =162a(5) =396a(6) =917a(7) =2036a(8) =4380a(9) =9152a(10) =18694a(11) =37380a(12) =73444a(13) =141918a(14) =270370a(15) =508178a(16) =943876a(17) =1733468a(18) =3151396a(19) =5674152a(20) =10126435a(21) =17921016a(22) =31468623a(23) =54848750a(24) =94935565a(25) =163232096a(26) =278903915a(27) =473693432a(28) =799949111a(29) =1343550666