21728091 has 48 divisors (see below), whose sum is σ = 38610432. Its totient is φ = 10602240.

The previous prime is 21728087. The next prime is 21728101. The reversal of 21728091 is 19082712.

21728091 = 29² + 30² + ... + 402².

It is not a de Polignac number, because 21728091 - 2² = 21728087 is a prime.

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21728011) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 42946 + ... + 43448.

It is an arithmetic number, because the mean of its divisors is an integer number (804384).

Almost surely, 2^21728091 is an apocalyptic number.

21728091 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21728091 is a deficient number, since it is larger than the sum of its proper divisors (16882341).

21728091 is a wasteful number, since it uses less digits than its factorization.

21728091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 552 (or 541 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 21728091 is about 4661.3400433781. The cubic root of 21728091 is about 279.0447507257.

The spelling of 21728091 in words is "twenty-one million, seven hundred twenty-eight thousand, ninety-one".