661680 has 60 divisors (see below), whose sum is σ = 2224560. Its totient is φ = 176256.

The previous prime is 661679. The next prime is 661697. The reversal of 661680 is 86166.

661680 = 128² + 129² + ... + 159².

It is a tau number, because it is divible by the number of its divisors (60).

It is a congruent number.

It is an unprimeable number.

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 11 ways as a sum of consecutive naturals, for example, 261 + ... + 1179.

It is an arithmetic number, because the mean of its divisors is an integer number (37076).

2⁶⁶¹⁶⁸⁰ is an apocalyptic number.

661680 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 661680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1112280).

661680 is an abundant number, since it is smaller than the sum of its proper divisors (1562880).

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

661680 is a wasteful number, since it uses less digits than its factorization.

661680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 938 (or 929 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 27.

The square root of 661680 is about 813.4371518440. The cubic root of 661680 is about 87.1396883966.

The spelling of 661680 in words is "six hundred sixty-one thousand, six hundred eighty".