20805217 has 4 divisors (see below), whose sum is σ = 20853700. Its totient is φ = 20756736.

The previous prime is 20805199. The next prime is 20805223. The reversal of 20805217 is 71250802.

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

It can be written as a sum of positive squares in 2 ways, for example, as 1934881 + 18870336 = 1391^2 + 4344^2 .

It is a cyclic number.

It is not a de Polignac number, because 20805217 - 2⁷ = 20805089 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 20805191 and 20805200.

It is not an unprimeable number, because it can be changed into a prime (20805287) 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, 23592 + ... + 24457.

It is an arithmetic number, because the mean of its divisors is an integer number (5213425).

Almost surely, 2^20805217 is an apocalyptic number.

It is an amenable number.

20805217 is a deficient number, since it is larger than the sum of its proper divisors (48483).

20805217 is an equidigital number, since it uses as much as digits as its factorization.

20805217 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48482.

The product of its (nonzero) digits is 1120, while the sum is 25.

The square root of 20805217 is about 4561.2736159981. The cubic root of 20805217 is about 275.0367642308.

The spelling of 20805217 in words is "twenty million, eight hundred five thousand, two hundred seventeen".