661644 has 18 divisors (see below), whose sum is σ = 1672580. Its totient is φ = 220536.

The previous prime is 661621. The next prime is 661663. The reversal of 661644 is 446166.

661644 is a `hidden beast` number, since 6 + 616 + 44 = 666.

It is a tau number, because it is divible by the number of its divisors (18).

It is a nude number because it is divisible by every one of its digits.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 9154 + ... + 9225.

2⁶⁶¹⁶⁴⁴ is an apocalyptic number.

It is an amenable number.

661644 is an abundant number, since it is smaller than the sum of its proper divisors (1010936).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

661644 is a wasteful number, since it uses less digits than its factorization.

661644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18389 (or 18384 counting only the distinct ones).

The product of its digits is 3456, while the sum is 27.

The square root of 661644 is about 813.4150232200. The cubic root of 661644 is about 87.1381080326.

The spelling of 661644 in words is "six hundred sixty-one thousand, six hundred forty-four".