816721691 has 8 divisors (see below), whose sum is σ = 850950144. Its totient is φ = 782985960.

The previous prime is 816721673. The next prime is 816721699. The reversal of 816721691 is 196127618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-816721691 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (816721699) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 119795 + ... + 126428.

It is an arithmetic number, because the mean of its divisors is an integer number (106368768).

Almost surely, 2^816721691 is an apocalyptic number.

816721691 is a deficient number, since it is larger than the sum of its proper divisors (34228453).

816721691 is a wasteful number, since it uses less digits than its factorization.

816721691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 246361.

The product of its digits is 36288, while the sum is 41.

The square root of 816721691 is about 28578.3430415411. The cubic root of 816721691 is about 934.7411528600.

The spelling of 816721691 in words is "eight hundred sixteen million, seven hundred twenty-one thousand, six hundred ninety-one".