1849

1849 = 43², a perfect square.

1849 is a centered octagonal number.

1849 is a perfect power in which neighboring digits are distinct.

1849 is a powerful number whose digit reversal is a semiprime: 9481 = 19 x 499.

Felix Klein (1849–1925) was born on April 25, 1849 (4/25/1849). Klein took particular delight in pointing out that each of the day (5²), month (2²), and year (43²) is the square of a prime number.


Source: The MacTutor History of Mathematics Archive
Image: Portrait Gallery