Second diagonal of A027539.

Terms

a(0) =15a(1) =160a(2) =935a(3) =4056a(4) =14763a(5) =48000a(6) =144495a(7) =411640a(8) =1125443a(9) =2980704a(10) =7696455a(11) =19463640a(12) =48370395a(13) =118431232a(14) =286252511a(15) =684101880a(16) =1618621875a(17) =3795700320a(18) =8829881655a(19) =20392492120a(20) =46787204555a(21) =106702788480a(22) =242010980175a(23) =546131512056