661904 has 20 divisors (see below), whose sum is σ = 1315020. Its totient is φ = 322560.

The previous prime is 661897. The next prime is 661909. The reversal of 661904 is 409166.

It can be written as a sum of positive squares in 2 ways, for example, as 102400 + 559504 = 320^2 + 748^2 .

It is not an unprimeable number, because it can be changed into a prime (661909) by changing a digit.

661904 is an untouchable number, because it is not equal to the sum of proper divisors of any 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 3 ways as a sum of consecutive naturals, for example, 152 + ... + 1160.

It is an arithmetic number, because the mean of its divisors is an integer number (65751).

2⁶⁶¹⁹⁰⁴ is an apocalyptic number.

It is an amenable number.

661904 is a deficient number, since it is larger than the sum of its proper divisors (653116).

661904 is a wasteful number, since it uses less digits than its factorization.

661904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1058 (or 1052 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 26.

The square root of 661904 is about 813.5748275359. The cubic root of 661904 is about 87.1495204846.

The spelling of 661904 in words is "six hundred sixty-one thousand, nine hundred four".