615991 has 4 divisors (see below), whose sum is σ = 618184. Its totient is φ = 613800.

The previous prime is 615971. The next prime is 615997. The reversal of 615991 is 199516.

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 615991 - 2⁹ = 615479 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 (615997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 600 + ... + 1261.

It is an arithmetic number, because the mean of its divisors is an integer number (154546).

2⁶¹⁵⁹⁹¹ is an apocalyptic number.

615991 is a deficient number, since it is larger than the sum of its proper divisors (2193).

615991 is a wasteful number, since it uses less digits than its factorization.

615991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2192.

The product of its digits is 2430, while the sum is 31.

The square root of 615991 is about 784.8509412621. The cubic root of 615991 is about 85.0860029184.

The spelling of 615991 in words is "six hundred fifteen thousand, nine hundred ninety-one".