Diagonal sums of number triangle A172380.

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =3a(5) =8a(6) =25a(7) =84a(8) =301a(9) =1139a(10) =4528a(11) =18849a(12) =81968a(13) =371622a(14) =1753164a(15) =8589608a(16) =43624741a(17) =229255133a(18) =1244544545a(19) =6968765313a(20) =40195073827a(21) =238527741350