a(n)=least k such that n begins at s(k), where s=A031324.

Terms

a(0) =1a(1) =2a(2) =3a(3) =11a(4) =4a(5) =25a(6) =23a(7) =5a(8) =15a(9) =26a(10) =55a(11) =1a(12) =6a(13) =16a(14) =31a(15) =42a(16) =52a(17) =40a(18) =78a(19) =98a(20) =8a(21) =93a(22) =2a(23) =118a(24) =35a(25) =106a(26) =132a(27) =57a(28) =94a(29) =113