Similar to A072921 but starting with 3.

Terms

a(0) =3a(1) =6a(2) =15a(3) =30a(4) =48a(5) =78a(6) =123a(7) =174a(8) =237a(9) =312a(10) =393a(11) =489a(12) =606a(13) =735a(14) =879a(15) =1047a(16) =1227a(17) =1419a(18) =1626a(19) =1848a(20) =2091a(21) =2346a(22) =2616a(23) =2901a(24) =3198a(25) =3516a(26) =3849a(27) =4206a(28) =4575a(29) =4965