66431551 has 4 divisors (see below), whose sum is σ = 66498400. Its totient is φ = 66364704.

The previous prime is 66431549. The next prime is 66431557. The reversal of 66431551 is 15513466.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 15513466 = 2 ⋅7756733.

It is a cyclic number.

It is not a de Polignac number, because 66431551 - 2¹ = 66431549 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 (66431557) 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, 31911 + ... + 33928.

It is an arithmetic number, because the mean of its divisors is an integer number (16624600).

Almost surely, 2^66431551 is an apocalyptic number.

66431551 is a deficient number, since it is larger than the sum of its proper divisors (66849).

66431551 is a wasteful number, since it uses less digits than its factorization.

66431551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66848.

The product of its digits is 10800, while the sum is 31.

The square root of 66431551 is about 8150.5552571589. Note that the first 3 decimals coincide. The cubic root of 66431551 is about 405.0028979115.

The spelling of 66431551 in words is "sixty-six million, four hundred thirty-one thousand, five hundred fifty-one".