21122991 has 32 divisors (see below), whose sum is σ = 33048000. Its totient is φ = 13313664.

The previous prime is 21122971. The next prime is 21123013. The reversal of 21122991 is 19922112.

It is not a de Polignac number, because 21122991 - 2⁷ = 21122863 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21122911) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 41245 + ... + 41753.

It is an arithmetic number, because the mean of its divisors is an integer number (1032750).

Almost surely, 2^21122991 is an apocalyptic number.

21122991 is a deficient number, since it is larger than the sum of its proper divisors (11925009).

21122991 is a wasteful number, since it uses less digits than its factorization.

21122991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 600 (or 594 counting only the distinct ones).

The product of its digits is 648, while the sum is 27.

The square root of 21122991 is about 4595.9755221280. The cubic root of 21122991 is about 276.4299772435.

The spelling of 21122991 in words is "twenty-one million, one hundred twenty-two thousand, nine hundred ninety-one".