81009001 has 2 divisors, whose sum is σ = 81009002. Its totient is φ = 81009000.

The previous prime is 81008971. The next prime is 81009007. The reversal of 81009001 is 10090018.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 75272976 + 5736025 = 8676^2 + 2395^2 .

It is a cyclic number.

It is not a de Polignac number, because 81009001 - 2⁹ = 81008489 is a prime.

It is the 9001-st Hogben number.

It is a self number, because there is not a number n which added to its sum of digits gives 81009001.

It is not a weakly prime, because it can be changed into another prime (81009007) by changing a digit.

It is a nontrivial repunit in base 9000.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40504500 + 40504501.

It is an arithmetic number, because the mean of its divisors is an integer number (40504501).

Almost surely, 2^81009001 is an apocalyptic number.

It is an amenable number.

81009001 is a deficient number, since it is larger than the sum of its proper divisors (1).

81009001 is an equidigital number, since it uses as much as digits as its factorization.

81009001 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 72, while the sum is 19.

The square root of 81009001 is about 9000.5000416644. The cubic root of 81009001 is about 432.6908972744.

Adding to 81009001 its reverse (10090018), we get a palindrome (91099019).

The spelling of 81009001 in words is "eighty-one million, nine thousand, one".