21728771 has 4 divisors (see below), whose sum is σ = 23006952. Its totient is φ = 20450592.

The previous prime is 21728747. The next prime is 21728789. The reversal of 21728771 is 17782712.

It is a semiprime because it is the product of two primes.

It is a de Polignac number, because none of the positive numbers 2^k-21728771 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21728741) 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 3 ways as a sum of consecutive naturals, for example, 639065 + ... + 639098.

It is an arithmetic number, because the mean of its divisors is an integer number (5751738).

Almost surely, 2^21728771 is an apocalyptic number.

21728771 is a deficient number, since it is larger than the sum of its proper divisors (1278181).

21728771 is a wasteful number, since it uses less digits than its factorization.

21728771 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1278180.

The product of its digits is 10976, while the sum is 35.

The square root of 21728771 is about 4661.4129832058. The cubic root of 21728771 is about 279.0476616801.

The spelling of 21728771 in words is "twenty-one million, seven hundred twenty-eight thousand, seven hundred seventy-one".