21701721 has 8 divisors (see below), whose sum is σ = 29717824. Its totient is φ = 14076720.

The previous prime is 21701689. The next prime is 21701723. The reversal of 21701721 is 12710712.

It is a happy number.

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

It is not a de Polignac number, because 21701721 - 2⁵ = 21701689 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 (21701723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 97645 + ... + 97866.

It is an arithmetic number, because the mean of its divisors is an integer number (3714728).

Almost surely, 2^21701721 is an apocalyptic number.

It is an amenable number.

21701721 is a deficient number, since it is larger than the sum of its proper divisors (8016103).

21701721 is a wasteful number, since it uses less digits than its factorization.

21701721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 195551.

The product of its (nonzero) digits is 196, while the sum is 21.

The square root of 21701721 is about 4658.5105988932. The cubic root of 21701721 is about 278.9318187475.

It can be divided in two parts, 21701 and 721, that added together give a palindrome (22422).

The spelling of 21701721 in words is "twenty-one million, seven hundred one thousand, seven hundred twenty-one".