Triangle arising in enumeration of maps on projective plane.

Terms

a(0) =1a(1) =5a(2) =9a(3) =22a(4) =112a(5) =118a(6) =93a(7) =899a(8) =2346a(9) =1773a(10) =386a(11) =5940a(12) =27446a(13) =48426a(14) =28650a(15) =1586a(16) =35138a(17) =247752a(18) =745180a(19) =995290a(20) =484578