691919891 has 4 divisors (see below), whose sum is σ = 745144512. Its totient is φ = 638695272.

The previous prime is 691919863. The next prime is 691919897. The reversal of 691919891 is 198919196.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-691919891 is a prime.

It is a super-2 number, since 2×691919891² = 957506271122903762, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (691919897) 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, 26612291 + ... + 26612316.

It is an arithmetic number, because the mean of its divisors is an integer number (186286128).

Almost surely, 2^691919891 is an apocalyptic number.

691919891 is a deficient number, since it is larger than the sum of its proper divisors (53224621).

691919891 is a wasteful number, since it uses less digits than its factorization.

691919891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53224620.

The product of its digits is 314928, while the sum is 53.

The square root of 691919891 is about 26304.3701882406. The cubic root of 691919891 is about 884.4744093176.

The spelling of 691919891 in words is "six hundred ninety-one million, nine hundred nineteen thousand, eight hundred ninety-one".