a(n) = t(n)_t(n) where t() = triangular numbers A000217.

Terms

a(0) =1a(1) =3a(2) =6a(3) =10a(4) =20a(5) =43a(6) =64a(7) =114a(8) =185a(9) =280a(10) =402a(11) =554a(12) =820a(13) =11030a(14) =14640a(15) =18910a(16) =24177a(17) =30439a(18) =37810a(19) =88410a(20) =107416a(21) =129286a(22) =154290a(23) =270000a(24) =317530a(25) =371359a(26) =431306a(27) =659350a(28) =758210a(29) =867695