661989 has 4 divisors (see below), whose sum is σ = 882656. Its totient is φ = 441324.

The previous prime is 661987. The next prime is 661993. The reversal of 661989 is 989166.

661989 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, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 661989 - 2¹ = 661987 is a prime.

It is a super-2 number, since 2×661989² = 876458872242, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661987) 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, 110329 + ... + 110334.

It is an arithmetic number, because the mean of its divisors is an integer number (220664).

2⁶⁶¹⁹⁸⁹ is an apocalyptic number.

It is an amenable number.

661989 is a deficient number, since it is larger than the sum of its proper divisors (220667).

661989 is a wasteful number, since it uses less digits than its factorization.

661989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 220666.

The product of its digits is 23328, while the sum is 39.

The square root of 661989 is about 813.6270644466. The cubic root of 661989 is about 87.1532508303.

The spelling of 661989 in words is "six hundred sixty-one thousand, nine hundred eighty-nine".