2021 = 43 x 47, the product of consecutive primes. Last happened in 1763 (= 41 x 43) and next in 2491 (= 47 x 53).
In the last 100 years these have been other special year when the year is a product of primes (ie it has exactly two prime factors, with four factors in total including 1 and itself).
- 1921, 1923, 1927, 1929
- 1934, 1937, 1939
- 1941, 1942, 1943, 1945
- 1954, 1957, 1959
- 1961, 1963, 1966, 1967, 1969
- 1977
- 1981, 1982, 1983, 1985
- 1991, 1994
- 2005
- 2018, 2019
