89

89 is a prime number.

89 is the smallest prime whose digits, 8 and 9, are composites.

89 is the eleventh Fibonacci number.

89 is the only two-digit number that is the sum of its first digit and its second digit squared: 8 + 9² = 89.

A sunflower head often displays florets in spirals of 55 and 89 around the outside.

Source: Number Gossip