a(n) = sum of the numbers between the two n's in A026280.

Terms

a(0) =9a(1) =13a(2) =18a(3) =24a(4) =39a(5) =57a(6) =78a(7) =102a(8) =117a(9) =146a(10) =164a(11) =198a(12) =219a(13) =258a(14) =282a(15) =326a(16) =373a(17) =402a(18) =454a(19) =509a(20) =543a(21) =603a(22) =666a(23) =705a(24) =773a(25) =844a(26) =888a(27) =964a(28) =1011a(29) =1092