Invert transform applied twice to Pascal's triangle A007318.

Terms

a(0) =1a(1) =1a(2) =1a(3) =3a(4) =6a(5) =3a(6) =9a(7) =27a(8) =27a(9) =9a(10) =27a(11) =108a(12) =162a(13) =108a(14) =27a(15) =81a(16) =405a(17) =810a(18) =810a(19) =405a(20) =81a(21) =243a(22) =1458a(23) =3645a(24) =4860a(25) =3645a(26) =1458a(27) =243a(28) =729a(29) =5103