399209221 has 2 divisors, whose sum is σ = 399209222. Its totient is φ = 399209220.

The previous prime is 399209219. The next prime is 399209297. The reversal of 399209221 is 122902993.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 398800900 + 408321 = 19970^2 + 639^2 .

It is a cyclic number.

It is not a de Polignac number, because 399209221 - 2¹ = 399209219 is a prime.

Together with 399209219, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (399203221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 199604610 + 199604611.

It is an arithmetic number, because the mean of its divisors is an integer number (199604611).

Almost surely, 2^399209221 is an apocalyptic number.

It is an amenable number.

399209221 is a deficient number, since it is larger than the sum of its proper divisors (1).

399209221 is an equidigital number, since it uses as much as digits as its factorization.

399209221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 17496, while the sum is 37.

The square root of 399209221 is about 19980.2207445263. The cubic root of 399209221 is about 736.3204369548.

It can be divided in two parts, 39920 and 9221, that added together give a triangular number (49141 = T₃₁₃).

The spelling of 399209221 in words is "three hundred ninety-nine million, two hundred nine thousand, two hundred twenty-one".