640426387 has 4 divisors (see below), whose sum is σ = 642789856. Its totient is φ = 638062920.

The previous prime is 640426349. The next prime is 640426403. The reversal of 640426387 is 783624046.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 783624046 = 2 ⋅391812023.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-640426387 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (640426307) 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, 1181328 + ... + 1181869.

It is an arithmetic number, because the mean of its divisors is an integer number (160697464).

Almost surely, 2^640426387 is an apocalyptic number.

640426387 is a deficient number, since it is larger than the sum of its proper divisors (2363469).

640426387 is a wasteful number, since it uses less digits than its factorization.

640426387 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2363468.

The product of its (nonzero) digits is 193536, while the sum is 40.

The square root of 640426387 is about 25306.6470912288. The cubic root of 640426387 is about 861.9652133076.

The spelling of 640426387 in words is "six hundred forty million, four hundred twenty-six thousand, three hundred eighty-seven".