Number of 3 X 3 symmetric matrices with row and column sums <= n.

Terms

a(0) =1a(1) =14a(2) =85a(3) =336a(4) =1023a(5) =2610a(6) =5860a(7) =11942a(8) =22555a(9) =40068a(10) =67677a(11) =109578a(12) =171157a(13) =259196a(14) =382096a(15) =550116a(16) =775629a(17) =1073394a(18) =1460845a(19) =1958396a(20) =2589763a(21) =3382302a(22) =4367364a(23) =5580666a(24) =7062679a(25) =8859032a(26) =11020933a(27) =13605606a(28) =16676745a(29) =20304984