1821661 has 4 divisors (see below), whose sum is σ = 1844800. Its totient is φ = 1798524.

The previous prime is 1821649. The next prime is 1821679. The reversal of 1821661 is 1661281.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1821661 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 (1821641) 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, 11451 + ... + 11608.

It is an arithmetic number, because the mean of its divisors is an integer number (461200).

2^1821661 is an apocalyptic number.

It is an amenable number.

1821661 is a deficient number, since it is larger than the sum of its proper divisors (23139).

1821661 is an equidigital number, since it uses as much as digits as its factorization.

1821661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23138.

The product of its digits is 576, while the sum is 25.

The square root of 1821661 is about 1349.6892234881. The cubic root of 1821661 is about 122.1300458666.

The spelling of 1821661 in words is "one million, eight hundred twenty-one thousand, six hundred sixty-one".