16521209 has 2 divisors, whose sum is σ = 16521210. Its totient is φ = 16521208.

The previous prime is 16521187. The next prime is 16521217. The reversal of 16521209 is 90212561.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15429184 + 1092025 = 3928^2 + 1045^2 .

It is an emirp because it is prime and its reverse (90212561) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16521209 - 2¹² = 16517113 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (16521259) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8260604 + 8260605.

It is an arithmetic number, because the mean of its divisors is an integer number (8260605).

Almost surely, 2^16521209 is an apocalyptic number.

It is an amenable number.

16521209 is a deficient number, since it is larger than the sum of its proper divisors (1).

16521209 is an equidigital number, since it uses as much as digits as its factorization.

16521209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1080, while the sum is 26.

The square root of 16521209 is about 4064.6290113613. The cubic root of 16521209 is about 254.6912012384.

The spelling of 16521209 in words is "sixteen million, five hundred twenty-one thousand, two hundred nine".