6561994181 has 2 divisors, whose sum is σ = 6561994182. Its totient is φ = 6561994180.

The previous prime is 6561994171. The next prime is 6561994217. The reversal of 6561994181 is 1814991656.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 4724500225 + 1837493956 = 68735^2 + 42866^2 .

It is a cyclic number.

It is not a de Polignac number, because 6561994181 - 2²² = 6557799877 is a prime.

It is a super-2 number, since 2×6561994181² = 86119535262955721522, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6561994171) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3280997090 + 3280997091.

It is an arithmetic number, because the mean of its divisors is an integer number (3280997091).

Almost surely, 2^6561994181 is an apocalyptic number.

It is an amenable number.

6561994181 is a deficient number, since it is larger than the sum of its proper divisors (1).

6561994181 is an equidigital number, since it uses as much as digits as its factorization.

6561994181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 466560, while the sum is 50.

The square root of 6561994181 is about 81006.1366872905. The cubic root of 6561994181 is about 1872.1699938044.

The spelling of 6561994181 in words is "six billion, five hundred sixty-one million, nine hundred ninety-four thousand, one hundred eighty-one".