209516921 has 2 divisors, whose sum is σ = 209516922. Its totient is φ = 209516920.

The previous prime is 209516911. The next prime is 209516939. The reversal of 209516921 is 129615902.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 188677696 + 20839225 = 13736^2 + 4565^2 .

It is a cyclic number.

It is not a de Polignac number, because 209516921 - 2¹⁰ = 209515897 is a prime.

It is not a weakly prime, because it can be changed into another prime (209516911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104758460 + 104758461.

It is an arithmetic number, because the mean of its divisors is an integer number (104758461).

Almost surely, 2^209516921 is an apocalyptic number.

It is an amenable number.

209516921 is a deficient number, since it is larger than the sum of its proper divisors (1).

209516921 is an equidigital number, since it uses as much as digits as its factorization.

209516921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 9720, while the sum is 35.

The square root of 209516921 is about 14474.6993405735. The cubic root of 209516921 is about 593.9360701262.

It can be divided in two parts, 20951 and 6921, that added together give a palindrome (27872).

The spelling of 209516921 in words is "two hundred nine million, five hundred sixteen thousand, nine hundred twenty-one".