a(1) = 1; thereafter a(n+1) = floor(sqrt(2*a(n)*(a(n)+1))).

Terms

a(0) =1a(1) =2a(2) =3a(3) =4a(4) =6a(5) =9a(6) =13a(7) =19a(8) =27a(9) =38a(10) =54a(11) =77a(12) =109a(13) =154a(14) =218a(15) =309a(16) =437a(17) =618a(18) =874a(19) =1236a(20) =1748a(21) =2472a(22) =3496a(23) =4944a(24) =6992a(25) =9888a(26) =13984a(27) =19777a(28) =27969a(29) =39554