1809721421 has 4 divisors (see below), whose sum is σ = 1814234844. Its totient is φ = 1805208000.

The previous prime is 1809721409. The next prime is 1809721429. The reversal of 1809721421 is 1241279081.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1241279081 = 7 ⋅177325583.

It can be written as a sum of positive squares in 2 ways, for example, as 922336900 + 887384521 = 30370^2 + 29789^2 .

It is a cyclic number.

It is not a de Polignac number, because 1809721421 - 2⁶ = 1809721357 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 (1809721429) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2256110 + ... + 2256911.

It is an arithmetic number, because the mean of its divisors is an integer number (453558711).

Almost surely, 2^1809721421 is an apocalyptic number.

It is an amenable number.

1809721421 is a deficient number, since it is larger than the sum of its proper divisors (4513423).

1809721421 is an equidigital number, since it uses as much as digits as its factorization.

1809721421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4513422.

The product of its (nonzero) digits is 8064, while the sum is 35.

The square root of 1809721421 is about 42540.8206432363. The cubic root of 1809721421 is about 1218.6263813043.

The spelling of 1809721421 in words is "one billion, eight hundred nine million, seven hundred twenty-one thousand, four hundred twenty-one".