666431551 has 4 divisors (see below), whose sum is σ = 667871392. Its totient is φ = 664991712.

The previous prime is 666431539. The next prime is 666431561. The reversal of 666431551 is 155134666.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 155134666 = 2 ⋅77567333.

It is a cyclic number.

It is not a de Polignac number, because 666431551 - 2²³ = 658042943 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 666431551.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666431561) 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, 719226 + ... + 720151.

It is an arithmetic number, because the mean of its divisors is an integer number (166967848).

Almost surely, 2^666431551 is an apocalyptic number.

666431551 is a deficient number, since it is larger than the sum of its proper divisors (1439841).

666431551 is a wasteful number, since it uses less digits than its factorization.

666431551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1439840.

The product of its digits is 64800, while the sum is 37.

The square root of 666431551 is about 25815.3355779080. The cubic root of 666431551 is about 873.4777564345.

The spelling of 666431551 in words is "six hundred sixty-six million, four hundred thirty-one thousand, five hundred fifty-one".