Third spoke of a hexagonal spiral.

Terms

a(0) =1a(1) =4a(2) =13a(3) =28a(4) =49a(5) =76a(6) =109a(7) =148a(8) =193a(9) =244a(10) =301a(11) =364a(12) =433a(13) =508a(14) =589a(15) =676a(16) =769a(17) =868a(18) =973a(19) =1084a(20) =1201a(21) =1324a(22) =1453a(23) =1588a(24) =1729a(25) =1876a(26) =2029a(27) =2188a(28) =2353a(29) =2524