81385921 has 2 divisors, whose sum is σ = 81385922. Its totient is φ = 81385920.

The previous prime is 81385867. The next prime is 81385933. The reversal of 81385921 is 12958318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 79014321 + 2371600 = 8889^2 + 1540^2 .

It is a cyclic number.

It is not a de Polignac number, because 81385921 - 2¹³ = 81377729 is a prime.

It is a Chen prime.

It is equal to p_4745719 and since 81385921 and 4745719 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (81385981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40692960 + 40692961.

It is an arithmetic number, because the mean of its divisors is an integer number (40692961).

Almost surely, 2^81385921 is an apocalyptic number.

It is an amenable number.

81385921 is a deficient number, since it is larger than the sum of its proper divisors (1).

81385921 is an equidigital number, since it uses as much as digits as its factorization.

81385921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 17280, while the sum is 37.

The square root of 81385921 is about 9021.4145786567. The cubic root of 81385921 is about 433.3609362430.

The spelling of 81385921 in words is "eighty-one million, three hundred eighty-five thousand, nine hundred twenty-one".