646921 has 8 divisors (see below), whose sum is σ = 736704. Its totient is φ = 562320.

The previous prime is 646913. The next prime is 646927. The reversal of 646921 is 129646.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 646921 - 2³ = 646913 is a prime.

It is a Duffinian number.

646921 is a lucky number.

It is a nialpdrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 646921.

It is not an unprimeable number, because it can be changed into a prime (646927) 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 7 ways as a sum of consecutive naturals, for example, 1026 + ... + 1531.

It is an arithmetic number, because the mean of its divisors is an integer number (92088).

2⁶⁴⁶⁹²¹ is an apocalyptic number.

It is an amenable number.

646921 is a deficient number, since it is larger than the sum of its proper divisors (89783).

646921 is a wasteful number, since it uses less digits than its factorization.

646921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2591.

The product of its digits is 2592, while the sum is 28.

The square root of 646921 is about 804.3139934130. The cubic root of 646921 is about 86.4869170631.

The spelling of 646921 in words is "six hundred forty-six thousand, nine hundred twenty-one".