21640646 has 4 divisors (see below), whose sum is σ = 32460972. Its totient is φ = 10820322.

The previous prime is 21640637. The next prime is 21640651. The reversal of 21640646 is 64604612.

It is a semiprime because it is the product of two primes.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5410160 + ... + 5410163.

It is an arithmetic number, because the mean of its divisors is an integer number (8115243).

Almost surely, 2^21640646 is an apocalyptic number.

21640646 is a deficient number, since it is larger than the sum of its proper divisors (10820326).

21640646 is a wasteful number, since it uses less digits than its factorization.

21640646 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10820325.

The product of its (nonzero) digits is 6912, while the sum is 29.

The square root of 21640646 is about 4651.9507736003. The cubic root of 21640646 is about 278.6699076135.

The spelling of 21640646 in words is "twenty-one million, six hundred forty thousand, six hundred forty-six".