21500000 has 84 divisors (see below), whose sum is σ = 54139932. Its totient is φ = 8400000.

The previous prime is 21499981. The next prime is 21500021. The reversal of 21500000 is 512.

It is a Harshad number since it is a multiple of its sum of digits (8).

It is a zygodrome in base 3.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 13 ways as a sum of consecutive naturals, for example, 499979 + ... + 500021.

It is an arithmetic number, because the mean of its divisors is an integer number (644523).

Almost surely, 2^21500000 is an apocalyptic number.

21500000 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 21500000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27069966).

21500000 is an abundant number, since it is smaller than the sum of its proper divisors (32639932).

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

21500000 is an frugal number, since it uses more digits than its factorization.

21500000 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 83 (or 50 counting only the distinct ones).

The product of its (nonzero) digits is 10, while the sum is 8.

The square root of 21500000 is about 4636.8092477479. The cubic root of 21500000 is about 278.0648883261.

Adding to 21500000 its reverse (512), we get a palindrome (21500512).

The spelling of 21500000 in words is "twenty-one million, five hundred thousand".