661890 has 16 divisors (see below), whose sum is σ = 1588608. Its totient is φ = 176496.

The previous prime is 661889. The next prime is 661897. The reversal of 661890 is 98166.

It is a Harshad number since it is a multiple of its sum of digits (30), and also a Moran number because the ratio is a prime number: 22063 = 661890 / (6 + 6 + 1 + 8 + 9 + 0).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661897) 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 7 ways as a sum of consecutive naturals, for example, 11002 + ... + 11061.

It is an arithmetic number, because the mean of its divisors is an integer number (99288).

2⁶⁶¹⁸⁹⁰ is an apocalyptic number.

661890 is an abundant number, since it is smaller than the sum of its proper divisors (926718).

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

661890 is a wasteful number, since it uses less digits than its factorization.

661890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22073.

The product of its (nonzero) digits is 2592, while the sum is 30.

The square root of 661890 is about 813.5662234877. The cubic root of 661890 is about 87.1489060441.

It can be divided in two parts, 661 and 890, that added together give a palindrome (1551).

The spelling of 661890 in words is "six hundred sixty-one thousand, eight hundred ninety".