NET
21 For although they knew God, they did not glorify him as God or give him thanks, but they became futile in their thoughts and their senseless hearts were darkened.
Darby
21 Because, knowing God, they glorified [him] not as God, neither were thankful; but fell into folly in their thoughts, and their heart without understanding was darkened:
KJV
21 Because that, when they knew God, they glorified [him] not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.