81866921 has 2 divisors, whose sum is σ = 81866922. Its totient is φ = 81866920.

The previous prime is 81866909. The next prime is 81866929. The reversal of 81866921 is 12966818.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 62410000 + 19456921 = 7900^2 + 4411^2 .

It is a cyclic number.

It is not a de Polignac number, because 81866921 - 2⁶ = 81866857 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81866929) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40933460 + 40933461.

It is an arithmetic number, because the mean of its divisors is an integer number (40933461).

Almost surely, 2^81866921 is an apocalyptic number.

It is an amenable number.

81866921 is a deficient number, since it is larger than the sum of its proper divisors (1).

81866921 is an equidigital number, since it uses as much as digits as its factorization.

81866921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 41472, while the sum is 41.

The square root of 81866921 is about 9048.0340958686. The cubic root of 81866921 is about 434.2129972347.

The spelling of 81866921 in words is "eighty-one million, eight hundred sixty-six thousand, nine hundred twenty-one".