A diagonal of triangle A291820.

Terms

a(0) =1a(1) =7a(2) =38a(3) =189a(4) =904a(5) =4242a(6) =19723a(7) =91366a(8) =423124a(9) =1963169a(10) =9138416a(11) =42718416a(12) =200656644a(13) =947423923a(14) =4497458118a(15) =21465533955a(16) =103001236168a(17) =496832195860