1816721 has 4 divisors (see below), whose sum is σ = 1819632. Its totient is φ = 1813812.

The previous prime is 1816699. The next prime is 1816729. The reversal of 1816721 is 1276181.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1276181 = 61 ⋅20921.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1816721 is a prime.

It is an alternating number because its digits alternate between odd and even.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1816729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 95 + ... + 1908.

It is an arithmetic number, because the mean of its divisors is an integer number (454908).

2^1816721 is an apocalyptic number.

It is an amenable number.

1816721 is a deficient number, since it is larger than the sum of its proper divisors (2911).

1816721 is an equidigital number, since it uses as much as digits as its factorization.

1816721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2910.

The product of its digits is 672, while the sum is 26.

The square root of 1816721 is about 1347.8579301989. The cubic root of 1816721 is about 122.0195480636.

The spelling of 1816721 in words is "one million, eight hundred sixteen thousand, seven hundred twenty-one".