21561739 has 4 divisors (see below), whose sum is σ = 21883624. Its totient is φ = 21239856.

The previous prime is 21561737. The next prime is 21561769. The reversal of 21561739 is 93716512.

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 21561739 - 2¹ = 21561737 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21561733) 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, 160842 + ... + 160975.

It is an arithmetic number, because the mean of its divisors is an integer number (5470906).

Almost surely, 2^21561739 is an apocalyptic number.

21561739 is a deficient number, since it is larger than the sum of its proper divisors (321885).

21561739 is an equidigital number, since it uses as much as digits as its factorization.

21561739 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 321884.

The product of its digits is 11340, while the sum is 34.

The square root of 21561739 is about 4643.4619628032. The cubic root of 21561739 is about 278.3307959498.

The spelling of 21561739 in words is "twenty-one million, five hundred sixty-one thousand, seven hundred thirty-nine".