Sum of numbers between the two n's in A026272.

Terms

a(0) =2a(1) =4a(2) =11a(3) =21a(4) =28a(5) =43a(6) =53a(7) =73a(8) =96a(9) =111a(10) =139a(11) =170a(12) =190a(13) =226a(14) =249a(15) =290a(16) =334a(17) =362a(18) =411a(19) =442a(20) =496a(21) =553a(22) =589a(23) =651a(24) =716a(25) =757a(26) =827a(27) =871a(28) =946a(29) =1024