AIG offers $690 million for rest of 21st Century

American International Group Inc. offered $690 million in cash for the shares of auto insurer 21st Century Insurance Group it doesn’t already own.

AIG proposed $19.75 a share, a 19% premium over Woodland Hills-based 21st Century’s closing price, the New York-based company said. AIG already owns 61.9% of the outstanding shares.