6 times heptagonal numbers: a(n) = 3*n*(5*n-3).

Terms

a(0) =0a(1) =6a(2) =42a(3) =108a(4) =204a(5) =330a(6) =486a(7) =672a(8) =888a(9) =1134a(10) =1410a(11) =1716a(12) =2052a(13) =2418a(14) =2814a(15) =3240a(16) =3696a(17) =4182a(18) =4698a(19) =5244a(20) =5820a(21) =6426a(22) =7062a(23) =7728a(24) =8424a(25) =9150a(26) =9906a(27) =10692a(28) =11508a(29) =12354