1566564721 has 4 divisors (see below), whose sum is σ = 1589946352. Its totient is φ = 1543183092.

The previous prime is 1566564697. The next prime is 1566564731. The reversal of 1566564721 is 1274656651.

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 not a de Polignac number, because 1566564721 - 2⁵ = 1566564689 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1566564731) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11690715 + ... + 11690848.

It is an arithmetic number, because the mean of its divisors is an integer number (397486588).

Almost surely, 2^1566564721 is an apocalyptic number.

It is an amenable number.

1566564721 is a deficient number, since it is larger than the sum of its proper divisors (23381631).

1566564721 is an equidigital number, since it uses as much as digits as its factorization.

1566564721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23381630.

The product of its digits is 302400, while the sum is 43.

The square root of 1566564721 is about 39579.8524630904. The cubic root of 1566564721 is about 1161.4025645138.

The spelling of 1566564721 in words is "one billion, five hundred sixty-six million, five hundred sixty-four thousand, seven hundred twenty-one".