20805709 has 4 divisors (see below), whose sum is σ = 20860416. Its totient is φ = 20751004.

The previous prime is 20805689. The next prime is 20805713. The reversal of 20805709 is 90750802.

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-20805709 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20805509) 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, 26779 + ... + 27544.

It is an arithmetic number, because the mean of its divisors is an integer number (5215104).

Almost surely, 2^20805709 is an apocalyptic number.

It is an amenable number.

20805709 is a deficient number, since it is larger than the sum of its proper divisors (54707).

20805709 is an equidigital number, since it uses as much as digits as its factorization.

20805709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 54706.

The product of its (nonzero) digits is 5040, while the sum is 31.

The square root of 20805709 is about 4561.3275479842. The cubic root of 20805709 is about 275.0389322291.

The spelling of 20805709 in words is "twenty million, eight hundred five thousand, seven hundred nine".