a(1) = 1, a(2) = 3; for n>2, a(n) = least value > a(n-1) such that pairwise differences are unique.

Terms

a(0) =1a(1) =3a(2) =4a(3) =8a(4) =14a(5) =22a(6) =31a(7) =46a(8) =62a(9) =82a(10) =108a(11) =137a(12) =149a(13) =171a(14) =206a(15) =259a(16) =303a(17) =367a(18) =414a(19) =479a(20) =545a(21) =578a(22) =658a(23) =728a(24) =848a(25) =921a(26) =1004a(27) =1130a(28) =1268a(29) =1352