21811955 has 8 divisors (see below), whose sum is σ = 28553904. Its totient is φ = 15863200.

The previous prime is 21811939. The next prime is 21811957. The reversal of 21811955 is 55911812.

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

It is not a de Polignac number, because 21811955 - 2⁴ = 21811939 is a prime.

It is a super-2 number, since 2×21811955² = 951522761844050, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21811957) 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, 198236 + ... + 198345.

It is an arithmetic number, because the mean of its divisors is an integer number (3569238).

Almost surely, 2^21811955 is an apocalyptic number.

21811955 is a deficient number, since it is larger than the sum of its proper divisors (6741949).

21811955 is a wasteful number, since it uses less digits than its factorization.

21811955 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 396597.

The product of its digits is 3600, while the sum is 32.

The square root of 21811955 is about 4670.3270763406. The cubic root of 21811955 is about 279.4032998707.

The spelling of 21811955 in words is "twenty-one million, eight hundred eleven thousand, nine hundred fifty-five".