1815564661 has 4 divisors (see below), whose sum is σ = 1849820652. Its totient is φ = 1781308672.

The previous prime is 1815564637. The next prime is 1815564671. The reversal of 1815564661 is 1664655181.

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

It can be written as a sum of positive squares in 2 ways, for example, as 835499025 + 980065636 = 28905^2 + 31306^2 .

It is a cyclic number.

It is not a de Polignac number, because 1815564661 - 2²³ = 1807176053 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 (1815564671) 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, 17127916 + ... + 17128021.

It is an arithmetic number, because the mean of its divisors is an integer number (462455163).

Almost surely, 2^1815564661 is an apocalyptic number.

It is an amenable number.

1815564661 is a deficient number, since it is larger than the sum of its proper divisors (34255991).

1815564661 is an equidigital number, since it uses as much as digits as its factorization.

1815564661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34255990.

The product of its digits is 172800, while the sum is 43.

The square root of 1815564661 is about 42609.4433312617. The cubic root of 1815564661 is about 1219.9365417589.

The spelling of 1815564661 in words is "one billion, eight hundred fifteen million, five hundred sixty-four thousand, six hundred sixty-one".