Even 9-gonal (nonagonal) pyramidal numbers.

Terms

a(0) =10a(1) =34a(2) =80a(3) =266a(4) =420a(5) =624a(6) =1210a(7) =1606a(8) =2080a(9) =3290a(10) =4040a(11) =4896a(12) =6954a(13) =8170a(14) =9520a(15) =12650a(16) =14444a(17) =16400a(18) =20826a(19) =23310a(20) =25984a(21) =31930a(22) =35216a(23) =38720a(24) =46410a(25) =50610a(26) =55056a(27) =64714a(28) =69940a(29) =75440