It was just a strange old penny, a copper-nickel Indian Head minted in 1859, when the government was trying out different metals for one-cent pieces. A grandfather gave it to Eric Pfeiffer Newman in 1918, when he was 7, a little bonus for his nickel-a-week allowance.

For almost a century, Mr. Newman called the fascinating old penny his first numismatic inspiration, a doorway to the past that took a boy from St. Louis into a life of curiosity, travel and adventure and made him one of America’s most distinguished authorities on the art and history of coinage and paper money.

He went on to scour the United States and visit more than 150 countries to explore the relationships between money and the societies and cultures it served. He died on Wednesday at his home just outside St. Louis, in Clayton, Mo., where he had lived all his life. He was 106.

To anyone who imagines that numismatists are hopeless romantics searching for coins in shipwrecks, musty attics and old curiosity shops, Mr. Newman was a composite antithesis: the author of books and scholarly articles and a consummate intellectual with an encyclopedic memory, a passion for history, the instincts of a relentless detective and the sharp eye of a trader in antiquarian treasures.