Negative-first-cousin-thrice-removed:
great-grandparent or
great-grandchild.
My
great-grandparent is my N1C3R
in theory and my
great-grandchild is also my N1C3R in theory.
Negative-first-cousin-six-times-removed: great-great-great-great-grandparent or great-great-great-great-grandchild.
My great-great-great-great-grandparent is my N1C6R
in theory and my great-great-great-great-grandchild is also my N1C6R
in theory.