661921 has 8 divisors (see below), whose sum is σ = 725760. Its totient is φ = 599952.

The previous prime is 661909. The next prime is 661931. The reversal of 661921 is 129166.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 661921 - 2⁵ = 661889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661931) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 336 + ... + 1198.

It is an arithmetic number, because the mean of its divisors is an integer number (90720).

2⁶⁶¹⁹²¹ is an apocalyptic number.

It is an amenable number.

661921 is a deficient number, since it is larger than the sum of its proper divisors (63839).

661921 is a wasteful number, since it uses less digits than its factorization.

661921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 935.

The product of its digits is 648, while the sum is 25.

The square root of 661921 is about 813.5852751863. The cubic root of 661921 is about 87.1502665793.

The spelling of 661921 in words is "six hundred sixty-one thousand, nine hundred twenty-one".