21513739 has 4 divisors (see below), whose sum is σ = 23168656. Its totient is φ = 19858824.

The previous prime is 21513697. The next prime is 21513749. The reversal of 21513739 is 93731512.

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

It is a cyclic number.

It is not a de Polignac number, because 21513739 - 2⁹ = 21513227 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21513739.

It is not an unprimeable number, because it can be changed into a prime (21513749) 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, 827439 + ... + 827464.

It is an arithmetic number, because the mean of its divisors is an integer number (5792164).

Almost surely, 2^21513739 is an apocalyptic number.

21513739 is a deficient number, since it is larger than the sum of its proper divisors (1654917).

21513739 is a wasteful number, since it uses less digits than its factorization.

21513739 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1654916.

The product of its digits is 5670, while the sum is 31.

The square root of 21513739 is about 4638.2905256139. The cubic root of 21513739 is about 278.1241056908.

The spelling of 21513739 in words is "twenty-one million, five hundred thirteen thousand, seven hundred thirty-nine".