5 times triangular numbers: a(n) = 5*n*(n+1)/2.

Terms

a(0) =0a(1) =5a(2) =15a(3) =30a(4) =50a(5) =75a(6) =105a(7) =140a(8) =180a(9) =225a(10) =275a(11) =330a(12) =390a(13) =455a(14) =525a(15) =600a(16) =680a(17) =765a(18) =855a(19) =950a(20) =1050a(21) =1155a(22) =1265a(23) =1380a(24) =1500a(25) =1625a(26) =1755a(27) =1890a(28) =2030a(29) =2175