819642991 has 4 divisors (see below), whose sum is σ = 823762000. Its totient is φ = 815523984.

The previous prime is 819642961. The next prime is 819643003. The reversal of 819642991 is 199246918.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 819642991 - 2¹³ = 819634799 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 (819642961) 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, 2059206 + ... + 2059603.

It is an arithmetic number, because the mean of its divisors is an integer number (205940500).

Almost surely, 2^819642991 is an apocalyptic number.

819642991 is a deficient number, since it is larger than the sum of its proper divisors (4119009).

819642991 is a wasteful number, since it uses less digits than its factorization.

819642991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4119008.

The product of its digits is 279936, while the sum is 49.

The square root of 819642991 is about 28629.4078003720. The cubic root of 819642991 is about 935.8543064530.

The spelling of 819642991 in words is "eight hundred nineteen million, six hundred forty-two thousand, nine hundred ninety-one".