66431561 has 4 divisors (see below), whose sum is σ = 75921792. Its totient is φ = 56941332.

The previous prime is 66431557. The next prime is 66431569. The reversal of 66431561 is 16513466.

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 not a de Polignac number, because 66431561 - 2² = 66431557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66431569) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4745105 + ... + 4745118.

It is an arithmetic number, because the mean of its divisors is an integer number (18980448).

Almost surely, 2^66431561 is an apocalyptic number.

It is an amenable number.

66431561 is a deficient number, since it is larger than the sum of its proper divisors (9490231).

66431561 is an equidigital number, since it uses as much as digits as its factorization.

66431561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9490230.

The product of its digits is 12960, while the sum is 32.

The square root of 66431561 is about 8150.5558706140. Note that the first 3 decimals coincide. The cubic root of 66431561 is about 405.0029182333.

The spelling of 66431561 in words is "sixty-six million, four hundred thirty-one thousand, five hundred sixty-one".