661818 has 16 divisors (see below), whose sum is σ = 1342656. Its totient is φ = 217440.

The previous prime is 661777. The next prime is 661823. The reversal of 661818 is 818166.

661818 is a modest number, since divided by 1818 gives 66 as remainder.

It is an unprimeable number.

661818 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 318 + ... + 1193.

It is an arithmetic number, because the mean of its divisors is an integer number (83916).

2⁶⁶¹⁸¹⁸ is an apocalyptic number.

661818 is an abundant number, since it is smaller than the sum of its proper divisors (680838).

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

661818 is a wasteful number, since it uses less digits than its factorization.

661818 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1589.

The product of its digits is 2304, while the sum is 30.

The square root of 661818 is about 813.5219726596. The cubic root of 661818 is about 87.1457459275.

The spelling of 661818 in words is "six hundred sixty-one thousand, eight hundred eighteen".