Partial sums of A007202 (crystal ball sequence for hexagonal close-packing).

Terms

a(0) =1a(1) =14a(2) =71a(3) =224a(4) =547a(5) =1134a(6) =2101a(7) =3584a(8) =5741a(9) =8750a(10) =12811a(11) =18144a(12) =24991a(13) =33614a(14) =44297a(15) =57344a(16) =73081a(17) =91854a(18) =114031a(19) =140000a(20) =170171a(21) =204974a(22) =244861a(23) =290304a(24) =341797a(25) =399854a(26) =465011a(27) =537824a(28) =618871a(29) =708750