Arises from color-symmetrized counting of tensor invariants.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =5a(5) =13a(6) =29a(7) =48a(8) =114a(9) =301a(10) =579a(11) =1462a(12) =4198a(13) =9295a(14) =24184a(15) =73489a(16) =179879a(17) =488616a(18) =1540939a(19) =4086226a(20) =11540851a(21) =37515163a(22) =106101932a(23) =311122047a(24) =1037973223a(25) =3097496100a(26) =9407708340a(27) =32130072122a(28) =100356356885a(29) =314999307749