21655779 has 16 divisors (see below), whose sum is σ = 30240000. Its totient is φ = 13766816.

The previous prime is 21655759. The next prime is 21655787. The reversal of 21655779 is 97755612.

It is a cyclic number.

It is not a de Polignac number, because 21655779 - 2⁷ = 21655651 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21655779.

It is not an unprimeable number, because it can be changed into a prime (21655709) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5722 + ... + 8720.

It is an arithmetic number, because the mean of its divisors is an integer number (1890000).

Almost surely, 2^21655779 is an apocalyptic number.

21655779 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

21655779 is a deficient number, since it is larger than the sum of its proper divisors (8584221).

21655779 is a wasteful number, since it uses less digits than its factorization.

21655779 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3114.

The product of its digits is 132300, while the sum is 42.

The square root of 21655779 is about 4653.5770112893. The cubic root of 21655779 is about 278.7348491299.

The spelling of 21655779 in words is "twenty-one million, six hundred fifty-five thousand, seven hundred seventy-nine".