Differences between odd powers of 3 and the next smaller square.

Terms

a(0) =2a(1) =2a(2) =18a(3) =71a(4) =83a(5) =747a(6) =1679a(7) =7538a(8) =22394a(9) =65186a(10) =177578a(11) =370898a(12) =1497119a(13) =2428283a(14) =5285858a(15) =47572722a(16) =129918074a(17) =274553378a(18) =1128916463a(19) =2107864523a(20) =6892205234a(21) =25794120683a(22) =14732727599a(23) =132594548391a(24) =214986322034