661899 has 16 divisors (see below), whose sum is σ = 1033472. Its totient is φ = 368928.

The previous prime is 661897. The next prime is 661909. The reversal of 661899 is 998166.

It is not a de Polignac number, because 661899 - 2¹ = 661897 is a prime.

It is a super-2 number, since 2×661899² = 876220572402, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661897) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 537 + ... + 1269.

It is an arithmetic number, because the mean of its divisors is an integer number (64592).

2⁶⁶¹⁸⁹⁹ is an apocalyptic number.

661899 is a deficient number, since it is larger than the sum of its proper divisors (371573).

661899 is a wasteful number, since it uses less digits than its factorization.

661899 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 786.

The product of its digits is 23328, while the sum is 39.

The square root of 661899 is about 813.5717546720. The cubic root of 661899 is about 87.1493010425.

The spelling of 661899 in words is "six hundred sixty-one thousand, eight hundred ninety-nine".