50 State Quarters to form what is known as a "mule". Only sixteen of these specimens, produced on dollar planchets, escaped from the mint. A 2005 Minnesota double die quarter, as well as a 2005 Minnesota quarter with extra trees (another die error), have both triggered numismatic interest. An unusual die break on some 2005 Kansas quarters created a humpback bison. Relatively more common are Kansas quarters bearing the motto "IN GOD WE RUST." The United States produces proof coinage in circulating base metal and, since 1992, in separately sold sets with the dimes, quarters, and half-dollars in silver. For the silver issues,
What Is Life the first ex-Beatle to have two top-ten hits in the United States.<ref name="Mapes/Billboard">Jillian Mapes, "George Harrison's 10 Biggest Billboard Hits", billboard.com, 29 November 2011 (retrieved 4 June 2014).</ref> The single was a success internationally, climbing to number 1 in Switzerland and on Australia's "Go-Set" National Top 60, and reaching the top three elsewhere in Europe and in Canada.<ref name="Tsosrt/GH singles">"George Harrison (Song artist 225)", Tsort pages (retrieved 16 October 2012).</ref> In Britain, where Harrison had resisted issuing a single from "All Things Must Pass" until midway through January, "What Is Life" appeared on the B-side to "My Sweet Lord" –