21751721 has 8 divisors (see below), whose sum is σ = 24033024. Its totient is φ = 19581760.

The previous prime is 21751703. The next prime is 21751729. The reversal of 21751721 is 12715712.

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

It is a cyclic number.

It is not a de Polignac number, because 21751721 - 2¹⁰ = 21750697 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21751729) 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, 27425 + ... + 28206.

It is an arithmetic number, because the mean of its divisors is an integer number (3004128).

Almost surely, 2^21751721 is an apocalyptic number.

It is an amenable number.

21751721 is a deficient number, since it is larger than the sum of its proper divisors (2281303).

21751721 is a wasteful number, since it uses less digits than its factorization.

21751721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55671.

The product of its digits is 980, while the sum is 26.

The square root of 21751721 is about 4663.8740334619. The cubic root of 21751721 is about 279.1458708006.

The spelling of 21751721 in words is "twenty-one million, seven hundred fifty-one thousand, seven hundred twenty-one".