686639 has 2 divisors, whose sum is σ = 686640. Its totient is φ = 686638.

The previous prime is 686611. The next prime is 686669. The reversal of 686639 is 936686.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-686639 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (686669) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343319 + 343320.

It is an arithmetic number, because the mean of its divisors is an integer number (343320).

2⁶⁸⁶⁶³⁹ is an apocalyptic number.

686639 is a deficient number, since it is larger than the sum of its proper divisors (1).

686639 is an equidigital number, since it uses as much as digits as its factorization.

686639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 46656, while the sum is 38.

The square root of 686639 is about 828.6368323940. The cubic root of 686639 is about 88.2218489928.

Subtracting 686639 from its reverse (936686), we obtain a cube (250047 = 63³).

The spelling of 686639 in words is "six hundred eighty-six thousand, six hundred thirty-nine".