Triangular numbers plus quarter squares: n*(n+1)/2 + floor(n^2/4) (i.e., A000217(n) + A002620(n)).

Terms

a(0) =0a(1) =1a(2) =4a(3) =8a(4) =14a(5) =21a(6) =30a(7) =40a(8) =52a(9) =65a(10) =80a(11) =96a(12) =114a(13) =133a(14) =154a(15) =176a(16) =200a(17) =225a(18) =252a(19) =280a(20) =310a(21) =341a(22) =374a(23) =408a(24) =444a(25) =481a(26) =520a(27) =560a(28) =602a(29) =645