Numbers n such that A002088(n) is a triangular number.

Terms

a(0) =0a(1) =1a(2) =4a(3) =5a(4) =9a(5) =19a(6) =148a(7) =209a(8) =404a(9) =652a(10) =763a(11) =1739a(12) =2790a(13) =9551a(14) =11117a(15) =13173a(16) =25641a(17) =170003a(18) =181927a(19) =519900a(20) =3253342a(21) =4816257a(22) =7103608a(23) =8269588a(24) =64261168a(25) =177847445a(26) =294878941a(27) =819667577a(28) =844965349a(29) =2944185248