21721198 has 4 divisors (see below), whose sum is σ = 32581800. Its totient is φ = 10860598.

The previous prime is 21721187. The next prime is 21721201. The reversal of 21721198 is 89112712.

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

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5430298 + ... + 5430301.

It is an arithmetic number, because the mean of its divisors is an integer number (8145450).

Almost surely, 2^21721198 is an apocalyptic number.

21721198 is a deficient number, since it is larger than the sum of its proper divisors (10860602).

21721198 is a wasteful number, since it uses less digits than its factorization.

21721198 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10860601.

The product of its digits is 2016, while the sum is 31.

The square root of 21721198 is about 4660.6006050723. The cubic root of 21721198 is about 279.0152396364.

The spelling of 21721198 in words is "twenty-one million, seven hundred twenty-one thousand, one hundred ninety-eight".