21193721 has 8 divisors (see below), whose sum is σ = 22411200. Its totient is φ = 19986480.

The previous prime is 21193691. The next prime is 21193727. The reversal of 21193721 is 12739112.

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

It is a de Polignac number, because none of the positive numbers 2^k-21193721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21193727) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1916 + ... + 6786.

It is an arithmetic number, because the mean of its divisors is an integer number (2801400).

Almost surely, 2^21193721 is an apocalyptic number.

It is an amenable number.

21193721 is a deficient number, since it is larger than the sum of its proper divisors (1217479).

21193721 is a wasteful number, since it uses less digits than its factorization.

21193721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5119.

The product of its digits is 756, while the sum is 26.

The square root of 21193721 is about 4603.6638669651. The cubic root of 21193721 is about 276.7381739651.

The spelling of 21193721 in words is "twenty-one million, one hundred ninety-three thousand, seven hundred twenty-one".