81331649 has 4 divisors (see below), whose sum is σ = 92950464. Its totient is φ = 69712836.

The previous prime is 81331639. The next prime is 81331651. The reversal of 81331649 is 94613318.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81331649 - 2⁴ = 81331633 is a prime.

It is a super-2 number, since 2×81331649² = 13229674258118402, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81331639) 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 in 3 ways as a sum of consecutive naturals, for example, 5809397 + ... + 5809410.

It is an arithmetic number, because the mean of its divisors is an integer number (23237616).

Almost surely, 2^81331649 is an apocalyptic number.

It is an amenable number.

81331649 is a deficient number, since it is larger than the sum of its proper divisors (11618815).

81331649 is a wasteful number, since it uses less digits than its factorization.

81331649 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11618814.

The product of its digits is 15552, while the sum is 35.

The square root of 81331649 is about 9018.4061230353. The cubic root of 81331649 is about 433.2645862670.

The spelling of 81331649 in words is "eighty-one million, three hundred thirty-one thousand, six hundred forty-nine".