20513721 has 4 divisors (see below), whose sum is σ = 27351632. Its totient is φ = 13675812.

The previous prime is 20513687. The next prime is 20513729. The reversal of 20513721 is 12731502.

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 not a de Polignac number, because 20513721 - 2⁷ = 20513593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20513729) 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, 3418951 + ... + 3418956.

It is an arithmetic number, because the mean of its divisors is an integer number (6837908).

Almost surely, 2^20513721 is an apocalyptic number.

It is an amenable number.

20513721 is a deficient number, since it is larger than the sum of its proper divisors (6837911).

20513721 is an equidigital number, since it uses as much as digits as its factorization.

20513721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6837910.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 20513721 is about 4529.2075465803. The cubic root of 20513721 is about 273.7462308440.

The spelling of 20513721 in words is "twenty million, five hundred thirteen thousand, seven hundred twenty-one".