Place where n-th 1 occurs in A007337.

Terms

a(0) =1a(1) =3a(2) =7a(3) =13a(4) =20a(5) =29a(6) =40a(7) =53a(8) =67a(9) =83a(10) =101a(11) =121a(12) =142a(13) =165a(14) =190a(15) =216a(16) =244a(17) =274a(18) =306a(19) =339a(20) =374a(21) =411a(22) =450a(23) =490a(24) =532a(25) =576a(26) =622a(27) =669a(28) =718a(29) =769