643716020921 has 2 divisors, whose sum is σ = 643716020922. Its totient is φ = 643716020920.

The previous prime is 643716020891. The next prime is 643716020929. The reversal of 643716020921 is 129020617346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 327371642896 + 316344378025 = 572164^2 + 562445^2 .

It is a cyclic number.

It is not a de Polignac number, because 643716020921 - 2¹⁴ = 643716004537 is a prime.

It is not a weakly prime, because it can be changed into another prime (643716020929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321858010460 + 321858010461.

It is an arithmetic number, because the mean of its divisors is an integer number (321858010461).

Almost surely, 2^643716020921 is an apocalyptic number.

It is an amenable number.

643716020921 is a deficient number, since it is larger than the sum of its proper divisors (1).

643716020921 is an equidigital number, since it uses as much as digits as its factorization.

643716020921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 108864, while the sum is 41.

The spelling of 643716020921 in words is "six hundred forty-three billion, seven hundred sixteen million, twenty thousand, nine hundred twenty-one".