81491009 has 2 divisors, whose sum is σ = 81491010. Its totient is φ = 81491008.

The previous prime is 81490973. The next prime is 81491021. The reversal of 81491009 is 90019418.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 76177984 + 5313025 = 8728^2 + 2305^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81491009 is a prime.

It is not a weakly prime, because it can be changed into another prime (81491029) 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, 40745504 + 40745505.

It is an arithmetic number, because the mean of its divisors is an integer number (40745505).

Almost surely, 2^81491009 is an apocalyptic number.

It is an amenable number.

81491009 is a deficient number, since it is larger than the sum of its proper divisors (1).

81491009 is an equidigital number, since it uses as much as digits as its factorization.

81491009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2592, while the sum is 32.

The square root of 81491009 is about 9027.2370634652. The cubic root of 81491009 is about 433.5473790013.

The spelling of 81491009 in words is "eighty-one million, four hundred ninety-one thousand, nine".