a(n) is the least k such that the remainder when 1000^k is divided by k is n.

Terms

a(0) =3a(1) =62a(2) =997a(3) =6a(4) =115a(5) =7a(6) =51a(7) =14a(8) =991a(9) =11a(10) =23a(11) =13a(12) =21a(13) =17a(14) =197a(15) =24a(16) =983a(17) =158a(18) =109a(19) =35a(20) =89a(21) =42a(22) =977a(23) =61a(24) =39a(25) =34a(26) =139a(27) =36a(28) =971a(29) =38