20020721 has 4 divisors (see below), whose sum is σ = 22880832. Its totient is φ = 17160612.

The previous prime is 20020711. The next prime is 20020723. The reversal of 20020721 is 12702002.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a de Polignac number, because none of the positive numbers 2^k-20020721 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20020696 and 20020705.

It is not an unprimeable number, because it can be changed into a prime (20020723) 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, 1430045 + ... + 1430058.

It is an arithmetic number, because the mean of its divisors is an integer number (5720208).

Almost surely, 2^20020721 is an apocalyptic number.

It is an amenable number.

20020721 is a deficient number, since it is larger than the sum of its proper divisors (2860111).

20020721 is an equidigital number, since it uses as much as digits as its factorization.

20020721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2860110.

The product of its (nonzero) digits is 56, while the sum is 14.

The square root of 20020721 is about 4474.4520334897. The cubic root of 20020721 is about 271.5354717166.

Adding to 20020721 its reverse (12702002), we get a palindrome (32722723).

The spelling of 20020721 in words is "twenty million, twenty thousand, seven hundred twenty-one".