20707721 has 4 divisors (see below), whose sum is σ = 21375744. Its totient is φ = 20039700.

The previous prime is 20707699. The next prime is 20707723. The reversal of 20707721 is 12770702.

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 cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20707721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (20707723) 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, 333965 + ... + 334026.

It is an arithmetic number, because the mean of its divisors is an integer number (5343936).

Almost surely, 2^20707721 is an apocalyptic number.

It is an amenable number.

20707721 is a deficient number, since it is larger than the sum of its proper divisors (668023).

20707721 is an equidigital number, since it uses as much as digits as its factorization.

20707721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 668022.

The product of its (nonzero) digits is 1372, while the sum is 26.

The square root of 20707721 is about 4550.5737000954. The cubic root of 20707721 is about 274.6064718360.

The spelling of 20707721 in words is "twenty million, seven hundred seven thousand, seven hundred twenty-one".