391639 has 2 divisors, whose sum is σ = 391640. Its totient is φ = 391638.

The previous prime is 391631. The next prime is 391661. The reversal of 391639 is 936193.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 391639 - 2³ = 391631 is a prime.

It is a super-2 number, since 2×391639² = 306762212642, which contains 22 as substring.

It is a Chen prime.

It is an Ulam number.

It is a self number, because there is not a number n which added to its sum of digits gives 391639.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (391631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 195819 + 195820.

It is an arithmetic number, because the mean of its divisors is an integer number (195820).

2³⁹¹⁶³⁹ is an apocalyptic number.

391639 is a deficient number, since it is larger than the sum of its proper divisors (1).

391639 is an equidigital number, since it uses as much as digits as its factorization.

391639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4374, while the sum is 31.

The square root of 391639 is about 625.8106742458. The cubic root of 391639 is about 73.1636411548.

The spelling of 391639 in words is "three hundred ninety-one thousand, six hundred thirty-nine".