643687549 has 2 divisors, whose sum is σ = 643687550. Its totient is φ = 643687548.

The previous prime is 643687537. The next prime is 643687553. The reversal of 643687549 is 945786346.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 620358649 + 23328900 = 24907^2 + 4830^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-643687549 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 643687496 and 643687505.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (643687579) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 321843774 + 321843775.

It is an arithmetic number, because the mean of its divisors is an integer number (321843775).

Almost surely, 2^643687549 is an apocalyptic number.

It is an amenable number.

643687549 is a deficient number, since it is larger than the sum of its proper divisors (1).

643687549 is an equidigital number, since it uses as much as digits as its factorization.

643687549 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4354560, while the sum is 52.

The square root of 643687549 is about 25370.9981869062. The cubic root of 643687549 is about 863.4258288851.

It can be divided in two parts, 64368 and 7549, that added together give a palindrome (71917).

The spelling of 643687549 in words is "six hundred forty-three million, six hundred eighty-seven thousand, five hundred forty-nine".