209797821 has 6 divisors (see below), whose sum is σ = 303041310. Its totient is φ = 139865208.

The previous prime is 209797813. The next prime is 209797877. The reversal of 209797821 is 128797902.

It can be written as a sum of positive squares in only one way, i.e., 167417721 + 42380100 = 12939^2 + 6510^2 .

It is not a de Polignac number, because 209797821 - 2³ = 209797813 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (209797321) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 11655426 + ... + 11655443.

It is an arithmetic number, because the mean of its divisors is an integer number (50506885).

Almost surely, 2^209797821 is an apocalyptic number.

It is an amenable number.

209797821 is a deficient number, since it is larger than the sum of its proper divisors (93243489).

209797821 is a wasteful number, since it uses less digits than its factorization.

209797821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23310875 (or 23310872 counting only the distinct ones).

The product of its (nonzero) digits is 127008, while the sum is 45.

The square root of 209797821 is about 14484.3992281351. The cubic root of 209797821 is about 594.2013822505.

The spelling of 209797821 in words is "two hundred nine million, seven hundred ninety-seven thousand, eight hundred twenty-one".