1661591 has 4 divisors (see below), whose sum is σ = 1696992. Its totient is φ = 1626192.

The previous prime is 1661587. The next prime is 1661599. The reversal of 1661591 is 1951661.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 1661591 - 2² = 1661587 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1661599) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17630 + ... + 17723.

It is an arithmetic number, because the mean of its divisors is an integer number (424248).

2^1661591 is an apocalyptic number.

1661591 is a deficient number, since it is larger than the sum of its proper divisors (35401).

1661591 is an equidigital number, since it uses as much as digits as its factorization.

1661591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35400.

The product of its digits is 1620, while the sum is 29.

The square root of 1661591 is about 1289.0271525457. The cubic root of 1661591 is about 118.4426303985.

The spelling of 1661591 in words is "one million, six hundred sixty-one thousand, five hundred ninety-one".