661905 has 16 divisors (see below), whose sum is σ = 1176960. Its totient is φ = 352944.

The previous prime is 661897. The next prime is 661909. The reversal of 661905 is 509166.

It is not a de Polignac number, because 661905 - 2³ = 661897 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (661909) 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, 2317 + ... + 2586.

It is an arithmetic number, because the mean of its divisors is an integer number (73560).

2⁶⁶¹⁹⁰⁵ is an apocalyptic number.

It is an amenable number.

661905 is a deficient number, since it is larger than the sum of its proper divisors (515055).

661905 is a wasteful number, since it uses less digits than its factorization.

661905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4917 (or 4911 counting only the distinct ones).

The product of its (nonzero) digits is 1620, while the sum is 27.

The square root of 661905 is about 813.5754421072. The cubic root of 661905 is about 87.1495643729.

The spelling of 661905 in words is "six hundred sixty-one thousand, nine hundred five".