641982821 has 4 divisors (see below), whose sum is σ = 642386412. Its totient is φ = 641579232.

The previous prime is 641982787. The next prime is 641982833. The reversal of 641982821 is 128289146.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 128289146 = 2 ⋅64144573.

It can be written as a sum of positive squares in 2 ways, for example, as 235960321 + 406022500 = 15361^2 + 20150^2 .

It is a cyclic number.

It is not a de Polignac number, because 641982821 - 2¹⁰ = 641981797 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (641982871) 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, 199400 + ... + 202593.

It is an arithmetic number, because the mean of its divisors is an integer number (160596603).

Almost surely, 2^641982821 is an apocalyptic number.

It is an amenable number.

641982821 is a deficient number, since it is larger than the sum of its proper divisors (403591).

641982821 is a wasteful number, since it uses less digits than its factorization.

641982821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 403590.

The product of its digits is 55296, while the sum is 41.

The square root of 641982821 is about 25337.3799158477. The cubic root of 641982821 is about 862.6629289906.

The spelling of 641982821 in words is "six hundred forty-one million, nine hundred eighty-two thousand, eight hundred twenty-one".