661399 has 4 divisors (see below), whose sum is σ = 663336. Its totient is φ = 659464.

The previous prime is 661393. The next prime is 661417. The reversal of 661399 is 993166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 993166 = 2 ⋅496583.

It is a cyclic number.

It is not a de Polignac number, because 661399 - 2⁹ = 660887 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661393) 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, 304 + ... + 1189.

It is an arithmetic number, because the mean of its divisors is an integer number (165834).

2⁶⁶¹³⁹⁹ is an apocalyptic number.

661399 is a deficient number, since it is larger than the sum of its proper divisors (1937).

661399 is a wasteful number, since it uses less digits than its factorization.

661399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1936.

The product of its digits is 8748, while the sum is 34.

The square root of 661399 is about 813.2644096479. The cubic root of 661399 is about 87.1273512550.

The spelling of 661399 in words is "six hundred sixty-one thousand, three hundred ninety-nine".