21811000 has 64 divisors (see below), whose sum is σ = 54082080. Its totient is φ = 8204800.

The previous prime is 21810991. The next prime is 21811001. The reversal of 21811000 is 11812.

21811000 is nontrivially palindromic in base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21811001) 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 15 ways as a sum of consecutive naturals, for example, 16359 + ... + 17641.

Almost surely, 2^21811000 is an apocalyptic number.

21811000 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21811000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27041040).

21811000 is an abundant number, since it is smaller than the sum of its proper divisors (32271080).

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

21811000 is a wasteful number, since it uses less digits than its factorization.

21811000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1321 (or 1307 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 13.

The square root of 21811000 is about 4670.2248339882. The cubic root of 21811000 is about 279.3992220756.

Adding to 21811000 its reverse (11812), we get a palindrome (21822812).

The spelling of 21811000 in words is "twenty-one million, eight hundred eleven thousand".