661979 has 4 divisors (see below), whose sum is σ = 696840. Its totient is φ = 627120.

The previous prime is 661961. The next prime is 661987. The reversal of 661979 is 979166.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-661979 is a prime.

It is an Ulam number.

It is a Duffinian number.

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

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17402 + ... + 17439.

It is an arithmetic number, because the mean of its divisors is an integer number (174210).

2⁶⁶¹⁹⁷⁹ is an apocalyptic number.

661979 is a deficient number, since it is larger than the sum of its proper divisors (34861).

661979 is a wasteful number, since it uses less digits than its factorization.

661979 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34860.

The product of its digits is 20412, while the sum is 38.

The square root of 661979 is about 813.6209191018. The cubic root of 661979 is about 87.1528119826.

The spelling of 661979 in words is "six hundred sixty-one thousand, nine hundred seventy-nine".