20709521 has 4 divisors (see below), whose sum is σ = 23668032. Its totient is φ = 17751012.

The previous prime is 20709511. The next prime is 20709523. The reversal of 20709521 is 12590702.

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 not a de Polignac number, because 20709521 - 2¹⁰ = 20708497 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 (20709523) 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, 1479245 + ... + 1479258.

It is an arithmetic number, because the mean of its divisors is an integer number (5917008).

Almost surely, 2^20709521 is an apocalyptic number.

It is an amenable number.

20709521 is a deficient number, since it is larger than the sum of its proper divisors (2958511).

20709521 is an equidigital number, since it uses as much as digits as its factorization.

20709521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2958510.

The product of its (nonzero) digits is 1260, while the sum is 26.

The square root of 20709521 is about 4550.7714730582. The cubic root of 20709521 is about 274.6144282456.

The spelling of 20709521 in words is "twenty million, seven hundred nine thousand, five hundred twenty-one".