20011721 has 4 divisors (see below), whose sum is σ = 20339844. Its totient is φ = 19683600.

The previous prime is 20011699. The next prime is 20011723. The reversal of 20011721 is 12711002.

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

It can be written as a sum of positive squares in 2 ways, for example, as 8526400 + 11485321 = 2920^2 + 3389^2 .

It is a cyclic number.

It is not a de Polignac number, because 20011721 - 2⁶ = 20011657 is a prime.

It is a super-3 number, since 3×20011721³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20011696 and 20011705.

It is not an unprimeable number, because it can be changed into a prime (20011723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 163970 + ... + 164091.

It is an arithmetic number, because the mean of its divisors is an integer number (5084961).

Almost surely, 2^20011721 is an apocalyptic number.

It is an amenable number.

20011721 is a deficient number, since it is larger than the sum of its proper divisors (328123).

20011721 is an equidigital number, since it uses as much as digits as its factorization.

20011721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 328122.

The product of its (nonzero) digits is 28, while the sum is 14.

The square root of 20011721 is about 4473.4462106971. The cubic root of 20011721 is about 271.4947774523.

Adding to 20011721 its reverse (12711002), we get a palindrome (32722723).

The spelling of 20011721 in words is "twenty million, eleven thousand, seven hundred twenty-one".