661879 has 2 divisors, whose sum is σ = 661880. Its totient is φ = 661878.

The previous prime is 661877. The next prime is 661883. The reversal of 661879 is 978166.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 661879 - 2¹ = 661877 is a prime.

Together with 661877, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661873) 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 as a sum of consecutive naturals, namely, 330939 + 330940.

It is an arithmetic number, because the mean of its divisors is an integer number (330940).

2⁶⁶¹⁸⁷⁹ is an apocalyptic number.

661879 is a deficient number, since it is larger than the sum of its proper divisors (1).

661879 is an equidigital number, since it uses as much as digits as its factorization.

661879 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 18144, while the sum is 37.

The square root of 661879 is about 813.5594631003. The cubic root of 661879 is about 87.1484232633.

It can be divided in two parts, 661 and 879, that added together give a triangular number (1540 = T₅₅).

The spelling of 661879 in words is "six hundred sixty-one thousand, eight hundred seventy-nine".