21090880 has 56 divisors (see below), whose sum is σ = 53190648. Its totient is φ = 7938048.

The previous prime is 21090871. The next prime is 21090889. The reversal of 21090880 is 8809012.

It is an interprime number because it is at equal distance from previous prime (21090871) and next prime (21090889).

It can be written as a sum of positive squares in 4 ways, for example, as 2359296 + 18731584 = 1536^2 + 4328^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21090889) 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, 3502 + ... + 7378.

It is an arithmetic number, because the mean of its divisors is an integer number (949833).

Almost surely, 2^21090880 is an apocalyptic number.

21090880 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 21090880, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26595324).

21090880 is an abundant number, since it is smaller than the sum of its proper divisors (32099768).

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

21090880 is a wasteful number, since it uses less digits than its factorization.

21090880 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3911 (or 3901 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 28.

The square root of 21090880 is about 4592.4808110650. The cubic root of 21090880 is about 276.2898306647.

Adding to 21090880 its reverse (8809012), we get a palindrome (29899892).

The spelling of 21090880 in words is "twenty-one million, ninety thousand, eight hundred eighty".