SEATTLE (AP) — Mark Zuckerberg and his wife, Priscilla Chan, were the most generous American philanthropists in 2013. According to the Chronicle of Philanthropy's annual list of the 50 top philanthropists, Zuckerberg and Chan topped the list with a donation of 18 million shares of Facebook stock, valued at more than $970 million, to a Silicon Valley nonprofit in December. The top 50 donors made donations last year totaling $7.7 billion, plus pledges of $2.9 billion. The Chronicle's editor says the most significant fact from the list was the amount of money coming from living donors, which totaled about the same amount as the two previous years combined. She says that's a sure sign the economy is getting better.