1665891 has 6 divisors (see below), whose sum is σ = 2406300. Its totient is φ = 1110588.

The previous prime is 1665889. The next prime is 1665899. The reversal of 1665891 is 1985661.

It is not a de Polignac number, because 1665891 - 2¹ = 1665889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1665899) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 92541 + ... + 92558.

It is an arithmetic number, because the mean of its divisors is an integer number (401050).

2^1665891 is an apocalyptic number.

1665891 is a deficient number, since it is larger than the sum of its proper divisors (740409).

1665891 is a wasteful number, since it uses less digits than its factorization.

1665891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 185105 (or 185102 counting only the distinct ones).

The product of its digits is 12960, while the sum is 36.

The square root of 1665891 is about 1290.6939993662. The cubic root of 1665891 is about 118.5447142051.

It can be divided in two parts, 1665 and 891, that added together give a triangular number (2556 = T₇₁).

The spelling of 1665891 in words is "one million, six hundred sixty-five thousand, eight hundred ninety-one".