1911

1911 = 3 x 7 x 7 x 13.

1911 is 11101110111 in base 2 (binary) (A023691), 131313 in base 4 (A037576), and 1133 in base 12 (A033010). It is 876 in base 15 and 777 in base 16 (A033029).

1911 is a hendecadonal number (A051682). It is also a heptagonal pyramidal number (A002413).

1911 divides 79³ - 1.

1911 was a year with exactly two "Friday the 13ths" (A190652).

Source: What's Special About This Number?

308

308 = 2 x 2 x 7 x 11.

308 is a heptagonal pyramidal number.

308 is the maximum number of regions into which 18 circles divide the plane.

308³ + 308⁰ + 308⁸ is a prime number.

308 is the sum of two consecutive primes: 308 = 151 + 157.

308 is 102102 in base 3. It is 464 in base 8.

Source: Prime Curios!

196

196 = 2² x 7².

196 is the smallest square that contains a multidigit prime number as a substring.

196 = 14² is a perfect square.

196 is the difference of two square numbers: 196 = 50² - 48².

The consecutive squares 13² = 169 and 14² = 196 use the same digits; 31² = 961 also uses the same digits.

196 has a unique representation as a sum of three squares: 196 = 4² + 6² + 12².

196 is a pentagonal pyramidal number and a heptagonal pyramidal number.

It is conjectured that 196 is the lowest Lychrel number. It is the lowest number not known to produce a palindrome by repeated reversal and addition. The algorithm has been tested to more than 246 million digits without finding a palindrome, but no one has ever proved that it will never produce one.

The Mercedes-Benz W196 was an entry in the 1954 and 1955 Formula One car racing series, winning 9 of 12 races.

Source: Number Gossip

880

880 = 2⁴ x 5 x 11.

880 is a heptagonal pyramidal number.

880 is the number of 4 x 4 magic squares.

880 is a number that can't be represented as a sum of three squares.

880 is 1177 in base 9.

880 Herba is an asteroid discovered in 1917.

Source: Number Gossip