640121555 has 8 divisors (see below), whose sum is σ = 768420000. Its totient is φ = 511914496.

The previous prime is 640121539. The next prime is 640121567. The reversal of 640121555 is 555121046.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 640121555 - 2⁴ = 640121539 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6350 + ... + 36339.

It is an arithmetic number, because the mean of its divisors is an integer number (96052500).

Almost surely, 2^640121555 is an apocalyptic number.

640121555 is a deficient number, since it is larger than the sum of its proper divisors (128298445).

640121555 is a wasteful number, since it uses less digits than its factorization.

640121555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 45693.

The product of its (nonzero) digits is 6000, while the sum is 29.

The square root of 640121555 is about 25300.6236089153. The cubic root of 640121555 is about 861.8284313733.

The spelling of 640121555 in words is "six hundred forty million, one hundred twenty-one thousand, five hundred fifty-five".