21929991 has 8 divisors (see below), whose sum is σ = 29263104. Its totient is φ = 14608440.

The previous prime is 21929987. The next prime is 21929993. The reversal of 21929991 is 19992912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21929991 - 2² = 21929987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21929993) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3660 + ... + 7566.

It is an arithmetic number, because the mean of its divisors is an integer number (3657888).

Almost surely, 2^21929991 is an apocalyptic number.

21929991 is a deficient number, since it is larger than the sum of its proper divisors (7333113).

21929991 is a wasteful number, since it uses less digits than its factorization.

21929991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5781.

The product of its digits is 26244, while the sum is 42.

The square root of 21929991 is about 4682.9468286539. The cubic root of 21929991 is about 279.9063930294.

The spelling of 21929991 in words is "twenty-one million, nine hundred twenty-nine thousand, nine hundred ninety-one".