391724521 has 2 divisors, whose sum is σ = 391724522. Its totient is φ = 391724520.

The previous prime is 391724519. The next prime is 391724563. The reversal of 391724521 is 125427193.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 364046400 + 27678121 = 19080^2 + 5261^2 .

It is a cyclic number.

It is not a de Polignac number, because 391724521 - 2¹ = 391724519 is a prime.

Together with 391724519, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (391724621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195862260 + 195862261.

It is an arithmetic number, because the mean of its divisors is an integer number (195862261).

Almost surely, 2^391724521 is an apocalyptic number.

It is an amenable number.

391724521 is a deficient number, since it is larger than the sum of its proper divisors (1).

391724521 is an equidigital number, since it uses as much as digits as its factorization.

391724521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15120, while the sum is 34.

The square root of 391724521 is about 19792.0317552292. The cubic root of 391724521 is about 731.6896627343.

The spelling of 391724521 in words is "three hundred ninety-one million, seven hundred twenty-four thousand, five hundred twenty-one".