Least k such that binomial(k, 2) >= binomial(2*n, n).

Terms

a(0) =2a(1) =3a(2) =4a(3) =7a(4) =13a(5) =23a(6) =44a(7) =84a(8) =161a(9) =313a(10) =609a(11) =1189a(12) =2327a(13) =4562a(14) =8958a(15) =17614a(16) =34673a(17) =68318a(18) =134724a(19) =265878a(20) =525066a(21) =1037554a(22) =2051390a(23) =4057939a(24) =8030892a(25) =15900354a(26) =31493446a(27) =62400953a(28) =123682583a(29) =245223436