691397939 has 4 divisors (see below), whose sum is σ = 732068424. Its totient is φ = 650727456.

The previous prime is 691397923. The next prime is 691397969. The reversal of 691397939 is 939793196.

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 691397939 - 2⁴ = 691397923 is a prime.

It is a super-2 number, since 2×691397939² = 956062220106895442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (691397969) 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, 20335217 + ... + 20335250.

It is an arithmetic number, because the mean of its divisors is an integer number (183017106).

Almost surely, 2^691397939 is an apocalyptic number.

691397939 is a deficient number, since it is larger than the sum of its proper divisors (40670485).

691397939 is a wasteful number, since it uses less digits than its factorization.

691397939 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40670484.

The product of its digits is 2480058, while the sum is 56.

The square root of 691397939 is about 26294.4469232574. The cubic root of 691397939 is about 884.2519513304.

The spelling of 691397939 in words is "six hundred ninety-one million, three hundred ninety-seven thousand, nine hundred thirty-nine".