661872 has 20 divisors (see below), whose sum is σ = 1709960. Its totient is φ = 220608.

The previous prime is 661849. The next prime is 661873. The reversal of 661872 is 278166.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661873) 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, 6847 + ... + 6942.

It is an arithmetic number, because the mean of its divisors is an integer number (85498).

2⁶⁶¹⁸⁷² is an apocalyptic number.

It is an amenable number.

661872 is an abundant number, since it is smaller than the sum of its proper divisors (1048088).

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

661872 is a wasteful number, since it uses less digits than its factorization.

661872 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13800 (or 13794 counting only the distinct ones).

The product of its digits is 4032, while the sum is 30.

The square root of 661872 is about 813.5551610063. Note that the first 3 decimals coincide. The cubic root of 661872 is about 87.1481160364.

The spelling of 661872 in words is "six hundred sixty-one thousand, eight hundred seventy-two".