Negative-first-cousin-twice-removed:
grandparent or
grandchild.
My
grandparent is my N1C2R
in theory and my
grandchild is also my N1C2R 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.