a(n) = A136431(n,n).

Terms

a(0) =0a(1) =1a(2) =3a(3) =11a(4) =41a(5) =155a(6) =591a(7) =2267a(8) =8735a(9) =33775a(10) =130965a(11) =509015a(12) =1982269a(13) =7732659a(14) =30208749a(15) =118167055a(16) =462760369a(17) =1814091011a(18) =7118044023a(19) =27952660883a(20) =109853552255a(21) =432021606103