Diagonal sums of number triangle A186826.

Terms

a(0) =1a(1) =1a(2) =4a(3) =14a(4) =57a(5) =247a(6) =1124a(7) =5296a(8) =25621a(9) =126529a(10) =635264a(11) =3232886a(12) =16638821a(13) =86456767a(14) =452927448a(15) =2389672752a(16) =12686560409a(17) =67721774737a(18) =363268546892