691323021 has 6 divisors (see below), whose sum is σ = 998577710. Its totient is φ = 460882008.

The previous prime is 691322963. The next prime is 691323089. The reversal of 691323021 is 120323196.

It can be written as a sum of positive squares in only one way, i.e., 629307396 + 62015625 = 25086^2 + 7875^2 .

It is not a de Polignac number, because 691323021 - 2¹⁰ = 691321997 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (691323221) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 38406826 + ... + 38406843.

Almost surely, 2^691323021 is an apocalyptic number.

It is an amenable number.

691323021 is a deficient number, since it is larger than the sum of its proper divisors (307254689).

691323021 is a wasteful number, since it uses less digits than its factorization.

691323021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 76813675 (or 76813672 counting only the distinct ones).

The product of its (nonzero) digits is 1944, while the sum is 27.

The square root of 691323021 is about 26293.0222872914. The cubic root of 691323021 is about 884.2200117980.

The spelling of 691323021 in words is "six hundred ninety-one million, three hundred twenty-three thousand, twenty-one".