21640428 has 36 divisors (see below), whose sum is σ = 54938520. Its totient is φ = 7182336.

The previous prime is 21640427. The next prime is 21640441. The reversal of 21640428 is 82404612.

It is a tau number, because it is divible by the number of its divisors (36).

It is not an unprimeable number, because it can be changed into a prime (21640427) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 8083 + ... + 10421.

It is an arithmetic number, because the mean of its divisors is an integer number (1526070).

Almost surely, 2^21640428 is an apocalyptic number.

It is an amenable number.

21640428 is an abundant number, since it is smaller than the sum of its proper divisors (33298092).

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

21640428 is a wasteful number, since it uses less digits than its factorization.

21640428 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2606 (or 2601 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 27.

The square root of 21640428 is about 4651.9273425108. The cubic root of 21640428 is about 278.6689718706.

The spelling of 21640428 in words is "twenty-one million, six hundred forty thousand, four hundred twenty-eight".