640215742 has 4 divisors (see below), whose sum is σ = 960323616. Its totient is φ = 320107870.

The previous prime is 640215739. The next prime is 640215799. The reversal of 640215742 is 247512046.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 247512046 = 2 ⋅123756023.

It is a super-2 number, since 2×640215742² = 819752392609221128, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 160053934 + ... + 160053937.

It is an arithmetic number, because the mean of its divisors is an integer number (240080904).

Almost surely, 2^640215742 is an apocalyptic number.

640215742 is a deficient number, since it is larger than the sum of its proper divisors (320107874).

640215742 is a wasteful number, since it uses less digits than its factorization.

640215742 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 320107873.

The product of its (nonzero) digits is 13440, while the sum is 31.

The square root of 640215742 is about 25302.4848977329. The cubic root of 640215742 is about 861.8706988942.

Adding to 640215742 its reverse (247512046), we get a palindrome (887727788).

The spelling of 640215742 in words is "six hundred forty million, two hundred fifteen thousand, seven hundred forty-two".