809218521 has 12 divisors (see below), whose sum is σ = 1169117872. Its totient is φ = 539365176.

The previous prime is 809218511. The next prime is 809218559. The reversal of 809218521 is 125812908.

It is not a de Polignac number, because 809218521 - 2⁶ = 809218457 is a prime.

It is a super-2 number, since 2×809218521² = 1309669229458854882, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (809218511) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 77790 + ... + 87576.

Almost surely, 2^809218521 is an apocalyptic number.

It is an amenable number.

809218521 is a deficient number, since it is larger than the sum of its proper divisors (359899351).

809218521 is a wasteful number, since it uses less digits than its factorization.

809218521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18980 (or 18977 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 36.

The square root of 809218521 is about 28446.7664418999. The cubic root of 809218521 is about 931.8698729859.

The spelling of 809218521 in words is "eight hundred nine million, two hundred eighteen thousand, five hundred twenty-one".