Pentagonal pyramidal numbers divisible by 3.

Terms

a(0) =0a(1) =6a(2) =18a(3) =75a(4) =126a(5) =288a(6) =405a(7) =726a(8) =936a(9) =1470a(10) =1800a(11) =2601a(12) =3078a(13) =4200a(14) =4851a(15) =6348a(16) =7200a(17) =9126a(18) =10206a(19) =12615a(20) =13950a(21) =16896a(22) =18513a(23) =22050a(24) =23976a(25) =28158a(26) =30420a(27) =35301a(28) =37926a(29) =43560