1566191981 has 4 divisors (see below), whose sum is σ = 1608521532. Its totient is φ = 1523862432.

The previous prime is 1566191971. The next prime is 1566191999. The reversal of 1566191981 is 1891916651.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1891916651 = 2221 ⋅851831.

It can be written as a sum of positive squares in 2 ways, for example, as 533148100 + 1033043881 = 23090^2 + 32141^2 .

It is a cyclic number.

It is not a de Polignac number, because 1566191981 - 2⁶ = 1566191917 is a prime.

It is a super-2 number, since 2×1566191981² = 4905914642697408722, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1566191971) 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, 21164720 + ... + 21164793.

It is an arithmetic number, because the mean of its divisors is an integer number (402130383).

Almost surely, 2^1566191981 is an apocalyptic number.

It is an amenable number.

1566191981 is a deficient number, since it is larger than the sum of its proper divisors (42329551).

1566191981 is an equidigital number, since it uses as much as digits as its factorization.

1566191981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42329550.

The product of its digits is 116640, while the sum is 47.

The square root of 1566191981 is about 39575.1434741556. The cubic root of 1566191981 is about 1161.3104445768.

The spelling of 1566191981 in words is "one billion, five hundred sixty-six million, one hundred ninety-one thousand, nine hundred eighty-one".