21721646 has 8 divisors (see below), whose sum is σ = 32746800. Its totient is φ = 10806048.

The previous prime is 21721621. The next prime is 21721717. The reversal of 21721646 is 64612712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26891 + ... + 27686.

It is an arithmetic number, because the mean of its divisors is an integer number (4093350).

Almost surely, 2^21721646 is an apocalyptic number.

21721646 is a deficient number, since it is larger than the sum of its proper divisors (11025154).

21721646 is a wasteful number, since it uses less digits than its factorization.

21721646 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 54778.

The product of its digits is 4032, while the sum is 29.

The square root of 21721646 is about 4660.6486672994. The cubic root of 21721646 is about 279.0171578542.

The spelling of 21721646 in words is "twenty-one million, seven hundred twenty-one thousand, six hundred forty-six".