21911991 has 8 divisors (see below), whose sum is σ = 29309424. Its totient is φ = 14561280.

The previous prime is 21911987. The next prime is 21912013. The reversal of 21911991 is 19911912.

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

It is not a de Polignac number, because 21911991 - 2² = 21911987 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21911971) 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, 10570 + ... + 12471.

It is an arithmetic number, because the mean of its divisors is an integer number (3663678).

Almost surely, 2^21911991 is an apocalyptic number.

21911991 is a deficient number, since it is larger than the sum of its proper divisors (7397433).

21911991 is a wasteful number, since it uses less digits than its factorization.

21911991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23361.

The product of its digits is 1458, while the sum is 33.

The square root of 21911991 is about 4681.0245673357. The cubic root of 21911991 is about 279.8297902593.

The spelling of 21911991 in words is "twenty-one million, nine hundred eleven thousand, nine hundred ninety-one".