21991455 has 72 divisors (see below), whose sum is σ = 43102800. Its totient is φ = 10340352.

The previous prime is 21991451. The next prime is 21991481. The reversal of 21991455 is 55419912.

It is not a de Polignac number, because 21991455 - 2² = 21991451 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991451) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 247051 + ... + 247139.

It is an arithmetic number, because the mean of its divisors is an integer number (598650).

Almost surely, 2^21991455 is an apocalyptic number.

21991455 is a deficient number, since it is larger than the sum of its proper divisors (21111345).

21991455 is a wasteful number, since it uses less digits than its factorization.

21991455 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 153 (or 133 counting only the distinct ones).

The product of its digits is 16200, while the sum is 36.

The square root of 21991455 is about 4689.5047712952. The cubic root of 21991455 is about 280.1676504493.

The spelling of 21991455 in words is "twenty-one million, nine hundred ninety-one thousand, four hundred fifty-five".