661864 has 32 divisors (see below), whose sum is σ = 1451520. Its totient is φ = 277056.

The previous prime is 661849. The next prime is 661873. The reversal of 661864 is 468166.

It is an unprimeable number.

661864 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, 2857 + ... + 3079.

It is an arithmetic number, because the mean of its divisors is an integer number (45360).

2⁶⁶¹⁸⁶⁴ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (725760).

661864 is an abundant number, since it is smaller than the sum of its proper divisors (789656).

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

661864 is a wasteful number, since it uses less digits than its factorization.

661864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 289 (or 285 counting only the distinct ones).

The product of its digits is 6912, while the sum is 31.

The square root of 661864 is about 813.5502442996. The cubic root of 661864 is about 87.1477649173.

The spelling of 661864 in words is "six hundred sixty-one thousand, eight hundred sixty-four".