21008910 has 64 divisors (see below), whose sum is σ = 54931968. Its totient is φ = 5111424.

The previous prime is 21008903. The next prime is 21008941. The reversal of 21008910 is 1980012.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 39909 + ... + 40431.

It is an arithmetic number, because the mean of its divisors is an integer number (858312).

Almost surely, 2^21008910 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21008910, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27465984).

21008910 is an abundant number, since it is smaller than the sum of its proper divisors (33923058).

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

21008910 is a wasteful number, since it uses less digits than its factorization.

21008910 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 649.

The product of its (nonzero) digits is 144, while the sum is 21.

The square root of 21008910 is about 4583.5477525602. The cubic root of 21008910 is about 275.9314311915.

Adding to 21008910 its reverse (1980012), we get a palindrome (22988922).

The spelling of 21008910 in words is "twenty-one million, eight thousand, nine hundred ten".