646621 has 4 divisors (see below), whose sum is σ = 650752. Its totient is φ = 642492.

The previous prime is 646619. The next prime is 646631. The reversal of 646621 is 126646.

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 646621 - 2¹ = 646619 is a prime.

It is a Duffinian number.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (646631) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1821 + ... + 2146.

It is an arithmetic number, because the mean of its divisors is an integer number (162688).

2⁶⁴⁶⁶²¹ is an apocalyptic number.

It is an amenable number.

646621 is a deficient number, since it is larger than the sum of its proper divisors (4131).

646621 is a wasteful number, since it uses less digits than its factorization.

646621 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4130.

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

The square root of 646621 is about 804.1274774562. The cubic root of 646621 is about 86.4735459885.

Adding to 646621 its sum of digits (25), we get a palindrome (646646).

The spelling of 646621 in words is "six hundred forty-six thousand, six hundred twenty-one".