21991911 has 16 divisors (see below), whose sum is σ = 31526400. Its totient is φ = 13592448.

The previous prime is 21991909. The next prime is 21991913. The reversal of 21991911 is 11919912.

It is an interprime number because it is at equal distance from previous prime (21991909) and next prime (21991913).

It is not a de Polignac number, because 21991911 - 2¹ = 21991909 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21991913) 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, 1426 + ... + 6783.

It is an arithmetic number, because the mean of its divisors is an integer number (1970400).

Almost surely, 2^21991911 is an apocalyptic number.

21991911 is a deficient number, since it is larger than the sum of its proper divisors (9534489).

21991911 is a wasteful number, since it uses less digits than its factorization.

21991911 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8278.

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

The square root of 21991911 is about 4689.5533902494. The cubic root of 21991911 is about 280.1695868918.

The spelling of 21991911 in words is "twenty-one million, nine hundred ninety-one thousand, nine hundred eleven".