21090000 has 200 divisors, whose sum is σ = 73601440. Its totient is φ = 5184000.

The previous prime is 21089993. The next prime is 21090007. The reversal of 21090000 is 9012.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21089993) and next prime (21090007).

It is a tau number, because it is divible by the number of its divisors (200).

It is a Harshad number since it is a multiple of its sum of digits (12).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21090007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 569982 + ... + 570018.

Almost surely, 2^21090000 is an apocalyptic number.

21090000 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 21090000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36800720).

21090000 is an abundant number, since it is smaller than the sum of its proper divisors (52511440).

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

21090000 is a wasteful number, since it uses less digits than its factorization.

21090000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 87 (or 66 counting only the distinct ones).

The product of its (nonzero) digits is 18, while the sum is 12.

The square root of 21090000 is about 4592.3850012820. The cubic root of 21090000 is about 276.2859879543.

Adding to 21090000 its reverse (9012), we get a palindrome (21099012).

The spelling of 21090000 in words is "twenty-one million, ninety thousand".