21320840 has 64 divisors (see below), whose sum is σ = 49863600. Its totient is φ = 8200192.

The previous prime is 21320837. The next prime is 21320851. The reversal of 21320840 is 4802312.

It can be written as a sum of positive squares in 8 ways, for example, as 2328676 + 18992164 = 1526^2 + 4358^2 .

It is a Harshad number since it is a multiple of its sum of digits (20).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 188624 + ... + 188736.

Almost surely, 2^21320840 is an apocalyptic number.

21320840 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 21320840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24931800).

21320840 is an abundant number, since it is smaller than the sum of its proper divisors (28542760).

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

21320840 is a wasteful number, since it uses less digits than its factorization.

21320840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 266 (or 262 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 20.

The square root of 21320840 is about 4617.4495124473. The cubic root of 21320840 is about 277.2903592087.

The spelling of 21320840 in words is "twenty-one million, three hundred twenty thousand, eight hundred forty".