691881021 has 24 divisors (see below), whose sum is σ = 1116125920. Its totient is φ = 425770992.

The previous prime is 691881017. The next prime is 691881089. The reversal of 691881021 is 120188196.

691881021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 691881021 - 2² = 691881017 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (691881221) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 106351 + ... + 112668.

Almost surely, 2^691881021 is an apocalyptic number.

It is an amenable number.

691881021 is a deficient number, since it is larger than the sum of its proper divisors (424244899).

691881021 is a wasteful number, since it uses less digits than its factorization.

691881021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 219047 (or 219035 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 36.

The square root of 691881021 is about 26303.6313272521. The cubic root of 691881021 is about 884.4578466275.

The spelling of 691881021 in words is "six hundred ninety-one million, eight hundred eighty-one thousand, twenty-one".