A377909 a(n) is the unmatched portion of the digit stream A376771 that A303656(n) must match, or -1 if this is the null string.
-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 9, 18, 810, 1017, 1719, 1989, 989100, 8910027, 91002726, 100272636, 272636199999999999, 7263619999999999911, 26361999999999991116, 636199999999999111620, 3619999999999911162015, 61999999999991116201512, 199999999999111620151224, 9999999999111620151224199
Offset: 1