21493840 has 40 divisors (see below), whose sum is σ = 51199848. Its totient is φ = 8386560.

The previous prime is 21493837. The next prime is 21493841. The reversal of 21493840 is 4839412.

It can be written as a sum of positive squares in 4 ways, for example, as 38416 + 21455424 = 196^2 + 4632^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is a hoax number, since the sum of its digits (31) coincides with the sum of the digits of its distinct prime factors.

It is a zygodrome in base 3.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21493841) 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, 4 + ... + 6556.

Almost surely, 2^21493840 is an apocalyptic number.

21493840 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 21493840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25599924).

21493840 is an abundant number, since it is smaller than the sum of its proper divisors (29706008).

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

21493840 is a wasteful number, since it uses less digits than its factorization.

21493840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6607 (or 6601 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 31.

The square root of 21493840 is about 4636.1449502793. The cubic root of 21493840 is about 278.0383295148.

The spelling of 21493840 in words is "twenty-one million, four hundred ninety-three thousand, eight hundred forty".