618991 has 2 divisors, whose sum is σ = 618992. Its totient is φ = 618990.

The previous prime is 618979. The next prime is 618997. The reversal of 618991 is 199816.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 618991 - 2¹¹ = 616943 is a prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (618997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 309495 + 309496.

It is an arithmetic number, because the mean of its divisors is an integer number (309496).

2⁶¹⁸⁹⁹¹ is an apocalyptic number.

618991 is a deficient number, since it is larger than the sum of its proper divisors (1).

618991 is an equidigital number, since it uses as much as digits as its factorization.

618991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3888, while the sum is 34.

The square root of 618991 is about 786.7598108699. The cubic root of 618991 is about 85.2239079313.

The spelling of 618991 in words is "six hundred eighteen thousand, nine hundred ninety-one".