661666 has 8 divisors (see below), whose sum is σ = 1013760. Its totient is φ = 323748.

The previous prime is 661663. The next prime is 661673. The reversal of 661666 is 666166.

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

It is a plaindrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (661663) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 3426 + ... + 3613.

It is an arithmetic number, because the mean of its divisors is an integer number (126720).

2⁶⁶¹⁶⁶⁶ is an apocalyptic number.

661666 is a deficient number, since it is larger than the sum of its proper divisors (352094).

661666 is a wasteful number, since it uses less digits than its factorization.

661666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7088.

The product of its digits is 7776, while the sum is 31.

The square root of 661666 is about 813.4285463395. The cubic root of 661666 is about 87.1390738174.

The spelling of 661666 in words is "six hundred sixty-one thousand, six hundred sixty-six".