Have you heard of Post Malone? If so, you probably aren’t a baby boomer.

According to data collected by the polling company YouGov, only 17% of US baby boomers, those born between 1946 and 1964, have heard of the bestselling rapper and songwriter. By contrast, 64% of millennials, those born between 1982 and 1999, have heard of him. That 47% difference places Malone among the top cultural touchstones that millennials know about and boomers most assuredly do not.

Malone isn’t even number one in recognition discrepancy. That spot is reserved for pop-rock band The All-American Rejects, which 74% of millennials have heard of, compared with only 23% of boomers. Musicians Skrillex and T-Pain come in for a close second and third.

The following chart shows the 20 bands, people, TV shows, apps, or games with the biggest chasms in recognition between generations. The data were collected betweenNovember 2017 and October 2018 and are based on about 8,000 respondents. The results are representative of the US population.

Just as enjoyable: the list of things boomers have heard of that millennials have not. Numbers one and two on this list are TV shows Marcus Welby, M.D. (1969-1976) and The Danny Thomas Show (1953-1965, officially titled Make Room for Daddy). These shows were the Big Bang Theory and Grey’s Anatomy of their day, but for millennials they are mostly lost to history.