646661 has 4 divisors (see below), whose sum is σ = 657324. Its totient is φ = 636000.

The previous prime is 646643. The next prime is 646669. The reversal of 646661 is 166646.

646661 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 256036 + 390625 = 506^2 + 625^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-646661 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a nialpdrome in base 7.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (646669) 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, 5240 + ... + 5361.

It is an arithmetic number, because the mean of its divisors is an integer number (164331).

2⁶⁴⁶⁶⁶¹ is an apocalyptic number.

646661 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

646661 is a deficient number, since it is larger than the sum of its proper divisors (10663).

646661 is a wasteful number, since it uses less digits than its factorization.

646661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10662.

The product of its digits is 5184, while the sum is 29.

The square root of 646661 is about 804.1523487499. The cubic root of 646661 is about 86.4753290373.

The spelling of 646661 in words is "six hundred forty-six thousand, six hundred sixty-one".