643542491 has 2 divisors, whose sum is σ = 643542492. Its totient is φ = 643542490.

The previous prime is 643542479. The next prime is 643542533. The reversal of 643542491 is 194245346.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 643542491 - 2²² = 639348187 is a prime.

It is not a weakly prime, because it can be changed into another prime (643542421) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321771245 + 321771246.

It is an arithmetic number, because the mean of its divisors is an integer number (321771246).

Almost surely, 2^643542491 is an apocalyptic number.

643542491 is a deficient number, since it is larger than the sum of its proper divisors (1).

643542491 is an equidigital number, since it uses as much as digits as its factorization.

643542491 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 103680, while the sum is 38.

The square root of 643542491 is about 25368.1392892739. The cubic root of 643542491 is about 863.3609649960.

The spelling of 643542491 in words is "six hundred forty-three million, five hundred forty-two thousand, four hundred ninety-one".