691388279 has 4 divisors (see below), whose sum is σ = 695792184. Its totient is φ = 686984376.

The previous prime is 691388261. The next prime is 691388293. The reversal of 691388279 is 972883196.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 691388279 - 2²⁸ = 422952823 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 691388279.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (691388239) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2201717 + ... + 2202030.

It is an arithmetic number, because the mean of its divisors is an integer number (173948046).

Almost surely, 2^691388279 is an apocalyptic number.

691388279 is a deficient number, since it is larger than the sum of its proper divisors (4403905).

691388279 is a wasteful number, since it uses less digits than its factorization.

691388279 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4403904.

The product of its digits is 1306368, while the sum is 53.

The square root of 691388279 is about 26294.2632336409. The cubic root of 691388279 is about 884.2478331455.

The spelling of 691388279 in words is "six hundred ninety-one million, three hundred eighty-eight thousand, two hundred seventy-nine".