643403921 has 2 divisors, whose sum is σ = 643403922. Its totient is φ = 643403920.

The previous prime is 643403861. The next prime is 643403927. The reversal of 643403921 is 129304346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 378886225 + 264517696 = 19465^2 + 16264^2 .

It is a cyclic number.

It is not a de Polignac number, because 643403921 - 2²² = 639209617 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (643403927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321701960 + 321701961.

It is an arithmetic number, because the mean of its divisors is an integer number (321701961).

Almost surely, 2^643403921 is an apocalyptic number.

It is an amenable number.

643403921 is a deficient number, since it is larger than the sum of its proper divisors (1).

643403921 is an equidigital number, since it uses as much as digits as its factorization.

643403921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 15552, while the sum is 32.

The square root of 643403921 is about 25365.4079604488. The cubic root of 643403921 is about 863.2989931664.

The spelling of 643403921 in words is "six hundred forty-three million, four hundred three thousand, nine hundred twenty-one".