a(n) = sigma(n,2) + sigma(n+1,2).

Terms

a(0) =6a(1) =15a(2) =31a(3) =47a(4) =76a(5) =100a(6) =135a(7) =176a(8) =221a(9) =252a(10) =332a(11) =380a(12) =420a(13) =510a(14) =601a(15) =631a(16) =745a(17) =817a(18) =908a(19) =1046a(20) =1110a(21) =1140a(22) =1380a(23) =1501a(24) =1501a(25) =1670a(26) =1870a(27) =1892a(28) =2142a(29) =2262