640820421 has 12 divisors (see below), whose sum is σ = 929048640. Its totient is φ = 425635560.

The previous prime is 640820413. The next prime is 640820431. The reversal of 640820421 is 124028046.

It is not a de Polignac number, because 640820421 - 2³ = 640820413 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640820431) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 128931 + ... + 133808.

It is an arithmetic number, because the mean of its divisors is an integer number (77420720).

Almost surely, 2^640820421 is an apocalyptic number.

It is an amenable number.

640820421 is a deficient number, since it is larger than the sum of its proper divisors (288228219).

640820421 is a wasteful number, since it uses less digits than its factorization.

640820421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 263016 (or 263013 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 27.

The square root of 640820421 is about 25314.4310818948. The cubic root of 640820421 is about 862.1419569970.

Adding to 640820421 its reverse (124028046), we get a palindrome (764848467).

The spelling of 640820421 in words is "six hundred forty million, eight hundred twenty thousand, four hundred twenty-one".