621991 has 4 divisors (see below), whose sum is σ = 627912. Its totient is φ = 616072.

The previous prime is 621983. The next prime is 621997. The reversal of 621991 is 199126.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199126 = 2 ⋅99563.

It is a cyclic number.

It is not a de Polignac number, because 621991 - 2³ = 621983 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 (621997) 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 in 3 ways as a sum of consecutive naturals, for example, 2800 + ... + 3013.

It is an arithmetic number, because the mean of its divisors is an integer number (156978).

2⁶²¹⁹⁹¹ is an apocalyptic number.

621991 is a deficient number, since it is larger than the sum of its proper divisors (5921).

621991 is a wasteful number, since it uses less digits than its factorization.

621991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5920.

The product of its digits is 972, while the sum is 28.

The square root of 621991 is about 788.6640602944. The cubic root of 621991 is about 85.3613680809.

The spelling of 621991 in words is "six hundred twenty-one thousand, nine hundred ninety-one".