20090721 has 16 divisors (see below), whose sum is σ = 30779264. Its totient is φ = 11418624.

The previous prime is 20090711. The next prime is 20090723. The reversal of 20090721 is 12709002.

It is a happy number.

It is not a de Polignac number, because 20090721 - 2⁵ = 20090689 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20090723) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1575 + ... + 6531.

It is an arithmetic number, because the mean of its divisors is an integer number (1923704).

Almost surely, 2^20090721 is an apocalyptic number.

20090721 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

20090721 is a deficient number, since it is larger than the sum of its proper divisors (10688543).

20090721 is a wasteful number, since it uses less digits than its factorization.

20090721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5160.

The product of its (nonzero) digits is 252, while the sum is 21.

The square root of 20090721 is about 4482.2673949688. The cubic root of 20090721 is about 271.8515671177.

Adding to 20090721 its reverse (12709002), we get a palindrome (32799723).

The spelling of 20090721 in words is "twenty million, ninety thousand, seven hundred twenty-one".