642661 has 4 divisors (see below), whose sum is σ = 663424. Its totient is φ = 621900.

The previous prime is 642623. The next prime is 642673. The reversal of 642661 is 166246.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 642661 - 2⁷ = 642533 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (642361) 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, 10335 + ... + 10396.

It is an arithmetic number, because the mean of its divisors is an integer number (165856).

2⁶⁴²⁶⁶¹ is an apocalyptic number.

It is an amenable number.

642661 is a deficient number, since it is larger than the sum of its proper divisors (20763).

642661 is a wasteful number, since it uses less digits than its factorization.

642661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20762.

The product of its digits is 1728, while the sum is 25.

The square root of 642661 is about 801.6613998441. The cubic root of 642661 is about 86.2966589242.

The spelling of 642661 in words is "six hundred forty-two thousand, six hundred sixty-one".