691387881 has 4 divisors (see below), whose sum is σ = 921850512. Its totient is φ = 460925252.

The previous prime is 691387877. The next prime is 691387973. The reversal of 691387881 is 188783196.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 691387881 - 2² = 691387877 is a prime.

It is a super-2 number, since 2×691387881² = 956034403987340322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (691387831) 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, 115231311 + ... + 115231316.

It is an arithmetic number, because the mean of its divisors is an integer number (230462628).

Almost surely, 2^691387881 is an apocalyptic number.

It is an amenable number.

691387881 is a deficient number, since it is larger than the sum of its proper divisors (230462631).

691387881 is a wasteful number, since it uses less digits than its factorization.

691387881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 230462630.

The product of its digits is 580608, while the sum is 51.

The square root of 691387881 is about 26294.2556654491. The cubic root of 691387881 is about 884.2476634720.

The spelling of 691387881 in words is "six hundred ninety-one million, three hundred eighty-seven thousand, eight hundred eighty-one".