391983521 has 2 divisors, whose sum is σ = 391983522. Its totient is φ = 391983520.

The previous prime is 391983491. The next prime is 391983523. The reversal of 391983521 is 125389193.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 305865121 + 86118400 = 17489^2 + 9280^2 .

It is a cyclic number.

It is not a de Polignac number, because 391983521 - 2¹⁸ = 391721377 is a prime.

Together with 391983523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (391983523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195991760 + 195991761.

It is an arithmetic number, because the mean of its divisors is an integer number (195991761).

Almost surely, 2^391983521 is an apocalyptic number.

It is an amenable number.

391983521 is a deficient number, since it is larger than the sum of its proper divisors (1).

391983521 is an equidigital number, since it uses as much as digits as its factorization.

391983521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 58320, while the sum is 41.

The square root of 391983521 is about 19798.5737112551. The cubic root of 391983521 is about 731.8508864699.

The spelling of 391983521 in words is "three hundred ninety-one million, nine hundred eighty-three thousand, five hundred twenty-one".