209921121 has 12 divisors (see below), whose sum is σ = 303427540. Its totient is φ = 139851360.

The previous prime is 209921113. The next prime is 209921123. The reversal of 209921121 is 121129902.

It can be written as a sum of positive squares in 2 ways, for example, as 111197025 + 98724096 = 10545^2 + 9936^2 .

It is not a de Polignac number, because 209921121 - 2³ = 209921113 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (209921123) 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, 7395 + ... + 21783.

Almost surely, 2^209921121 is an apocalyptic number.

It is an amenable number.

209921121 is a deficient number, since it is larger than the sum of its proper divisors (93506419).

209921121 is a wasteful number, since it uses less digits than its factorization.

209921121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16016 (or 16013 counting only the distinct ones).

The product of its (nonzero) digits is 648, while the sum is 27.

The square root of 209921121 is about 14488.6549065122. The cubic root of 209921121 is about 594.3177652233.

It can be divided in two parts, 2099 and 21121, that added together give a triangular number (23220 = T₂₁₅).

The spelling of 209921121 in words is "two hundred nine million, nine hundred twenty-one thousand, one hundred twenty-one".