643281791 has 2 divisors, whose sum is σ = 643281792. Its totient is φ = 643281790.

The previous prime is 643281761. The next prime is 643281811. The reversal of 643281791 is 197182346.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 643281791 - 2¹⁸ = 643019647 is a prime.

It is a super-2 number, since 2×643281791² = 827622925264335362, which contains 22 as substring.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643281731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321640895 + 321640896.

It is an arithmetic number, because the mean of its divisors is an integer number (321640896).

Almost surely, 2^643281791 is an apocalyptic number.

643281791 is a deficient number, since it is larger than the sum of its proper divisors (1).

643281791 is an equidigital number, since it uses as much as digits as its factorization.

643281791 is an evil number, because the sum of its binary digits is even.

The product of its digits is 72576, while the sum is 41.

The square root of 643281791 is about 25363.0004337026. Note that the first 3 decimals coincide. The cubic root of 643281791 is about 863.2443663219.

The spelling of 643281791 in words is "six hundred forty-three million, two hundred eighty-one thousand, seven hundred ninety-one".