Triangular arithmetic on half-squares: b(n)*(b(n) - 1)/2 where b(n) = floor(n^2/2).

Terms

a(0) =0a(1) =0a(2) =1a(3) =6a(4) =28a(5) =66a(6) =153a(7) =276a(8) =496a(9) =780a(10) =1225a(11) =1770a(12) =2556a(13) =3486a(14) =4753a(15) =6216a(16) =8128a(17) =10296a(18) =13041a(19) =16110a(20) =19900a(21) =24090a(22) =29161a(23) =34716a(24) =41328a(25) =48516a(26) =56953a(27) =66066a(28) =76636a(29) =87990