21811956 has 12 divisors (see below), whose sum is σ = 50894592. Its totient is φ = 7270648.

The previous prime is 21811939. The next prime is 21811957. The reversal of 21811956 is 65911812.

It is a tau number, because it is divible by the number of its divisors (12).

It is a super-2 number, since 2×21811956² = 951522849091872, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21811957) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 908820 + ... + 908843.

It is an arithmetic number, because the mean of its divisors is an integer number (4241216).

Almost surely, 2^21811956 is an apocalyptic number.

It is an amenable number.

21811956 is an abundant number, since it is smaller than the sum of its proper divisors (29082636).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21811956 is a wasteful number, since it uses less digits than its factorization.

21811956 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1817670 (or 1817668 counting only the distinct ones).

The product of its digits is 4320, while the sum is 33.

The square root of 21811956 is about 4670.3271833995. The cubic root of 21811956 is about 279.4033041405.

The spelling of 21811956 in words is "twenty-one million, eight hundred eleven thousand, nine hundred fifty-six".