643281811 has 2 divisors, whose sum is σ = 643281812. Its totient is φ = 643281810.

The previous prime is 643281791. The next prime is 643281833. The reversal of 643281811 is 118182346.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643281811 is a prime.

It is a super-2 number, since 2×643281811² = 827622976726879442, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (643281211) by changing a digit.

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 as a sum of consecutive naturals, namely, 321640905 + 321640906.

It is an arithmetic number, because the mean of its divisors is an integer number (321640906).

Almost surely, 2^643281811 is an apocalyptic number.

643281811 is a deficient number, since it is larger than the sum of its proper divisors (1).

643281811 is an equidigital number, since it uses as much as digits as its factorization.

643281811 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 9216, while the sum is 34.

The square root of 643281811 is about 25363.0008279777. Note that the first 3 decimals coincide. The cubic root of 643281811 is about 863.2443752681.

The spelling of 643281811 in words is "six hundred forty-three million, two hundred eighty-one thousand, eight hundred eleven".