Number of 2 X 2 0..n arrays with rows and columns in lexicographically nondecreasing order.

Terms

a(0) =7a(1) =29a(2) =86a(3) =205a(4) =421a(5) =777a(6) =1324a(7) =2121a(8) =3235a(9) =4741a(10) =6722a(11) =9269a(12) =12481a(13) =16465a(14) =21336a(15) =27217a(16) =34239a(17) =42541a(18) =52270a(19) =63581a(20) =76637a(21) =91609a(22) =108676a(23) =128025a(24) =149851a(25) =174357a(26) =201754a(27) =232261a(28) =266105a(29) =303521