a(n) = Sum_{k=1..n} tan(k*Pi/(1+2*n))^4.

Terms

a(0) =0a(1) =9a(2) =90a(3) =371a(4) =1044a(5) =2365a(6) =4654a(7) =8295a(8) =13736a(9) =21489a(10) =32130a(11) =46299a(12) =64700a(13) =88101a(14) =117334a(15) =153295a(16) =196944a(17) =249305a(18) =311466a(19) =384579a(20) =469860a(21) =568589a(22) =682110a(23) =811831a(24) =959224a(25) =1125825a(26) =1313234a(27) =1523115a(28) =1757196a(29) =2017269