Number of integer points in a certain quadrilateral scaled by a factor of n.

Terms

a(0) =2a(1) =4a(2) =7a(3) =11a(4) =16a(5) =21a(6) =28a(7) =35a(8) =43a(9) =52a(10) =62a(11) =72a(12) =84a(13) =96a(14) =109a(15) =123a(16) =138a(17) =153a(18) =170a(19) =187a(20) =205a(21) =224a(22) =244a(23) =264a(24) =286a(25) =308a(26) =331a(27) =355a(28) =380a(29) =405