6561881639 has 2 divisors, whose sum is σ = 6561881640. Its totient is φ = 6561881638.

The previous prime is 6561881621. The next prime is 6561881653. The reversal of 6561881639 is 9361881656.

6561881639 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6561881639 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6561881609) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3280940819 + 3280940820.

It is an arithmetic number, because the mean of its divisors is an integer number (3280940820).

Almost surely, 2^6561881639 is an apocalyptic number.

6561881639 is a deficient number, since it is larger than the sum of its proper divisors (1).

6561881639 is an equidigital number, since it uses as much as digits as its factorization.

6561881639 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1866240, while the sum is 53.

The square root of 6561881639 is about 81005.4420332363. The cubic root of 6561881639 is about 1872.1592908100.

The spelling of 6561881639 in words is "six billion, five hundred sixty-one million, eight hundred eighty-one thousand, six hundred thirty-nine".