81178921 has 2 divisors, whose sum is σ = 81178922. Its totient is φ = 81178920.

The previous prime is 81178871. The next prime is 81178931. The reversal of 81178921 is 12987118.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 47073321 + 34105600 = 6861^2 + 5840^2 .

It is a cyclic number.

It is not a de Polignac number, because 81178921 - 2⁷ = 81178793 is a prime.

It is not a weakly prime, because it can be changed into another prime (81178931) 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, 40589460 + 40589461.

It is an arithmetic number, because the mean of its divisors is an integer number (40589461).

Almost surely, 2^81178921 is an apocalyptic number.

It is an amenable number.

81178921 is a deficient number, since it is larger than the sum of its proper divisors (1).

81178921 is an equidigital number, since it uses as much as digits as its factorization.

81178921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8064, while the sum is 37.

The square root of 81178921 is about 9009.9345724594. The cubic root of 81178921 is about 432.9932154957.

The spelling of 81178921 in words is "eighty-one million, one hundred seventy-eight thousand, nine hundred twenty-one".