642491 has 4 divisors (see below), whose sum is σ = 649800. Its totient is φ = 635184.

The previous prime is 642487. The next prime is 642517. The reversal of 642491 is 194246.

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 642491 - 2² = 642487 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 642491.

It is not an unprimeable number, because it can be changed into a prime (642791) 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, 3521 + ... + 3698.

It is an arithmetic number, because the mean of its divisors is an integer number (162450).

2⁶⁴²⁴⁹¹ is an apocalyptic number.

642491 is a deficient number, since it is larger than the sum of its proper divisors (7309).

642491 is an equidigital number, since it uses as much as digits as its factorization.

642491 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7308.

The product of its digits is 1728, while the sum is 26.

The square root of 642491 is about 801.5553630287. Note that the first 3 decimals coincide. The cubic root of 642491 is about 86.2890490408.

The spelling of 642491 in words is "six hundred forty-two thousand, four hundred ninety-one".