691639 has 8 divisors (see below), whose sum is σ = 754992. Its totient is φ = 629760.

The previous prime is 691637. The next prime is 691651. The reversal of 691639 is 936196.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 691639 - 2¹ = 691637 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (691631) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 759 + ... + 1399.

It is an arithmetic number, because the mean of its divisors is an integer number (94374).

2⁶⁹¹⁶³⁹ is an apocalyptic number.

691639 is a deficient number, since it is larger than the sum of its proper divisors (63353).

691639 is a wasteful number, since it uses less digits than its factorization.

691639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 737.

The product of its digits is 8748, while the sum is 34.

The square root of 691639 is about 831.6483631920. The cubic root of 691639 is about 88.4354706381.

The spelling of 691639 in words is "six hundred ninety-one thousand, six hundred thirty-nine".