A diagonal of triangle defined in A059226.

Terms

a(0) =0a(1) =2a(2) =12a(3) =70a(4) =426a(5) =2708a(6) =17846a(7) =121014a(8) =839388a(9) =5929162a(10) =42509318a(11) =308561388a(12) =2263197114a(13) =16748071210a(14) =124893822012a(15) =937612685502