21439640 has 16 divisors (see below), whose sum is σ = 48239280. Its totient is φ = 8575840.

The previous prime is 21439633. The next prime is 21439643. The reversal of 21439640 is 4693412.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21439643) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 267956 + ... + 268035.

It is an arithmetic number, because the mean of its divisors is an integer number (3014955).

Almost surely, 2^21439640 is an apocalyptic number.

21439640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21439640 is an abundant number, since it is smaller than the sum of its proper divisors (26799640).

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

21439640 is a wasteful number, since it uses less digits than its factorization.

21439640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 536002 (or 535998 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 29.

The square root of 21439640 is about 4630.2958868738. The cubic root of 21439640 is about 277.8044274284.

The spelling of 21439640 in words is "twenty-one million, four hundred thirty-nine thousand, six hundred forty".