81733921 has 4 divisors (see below), whose sum is σ = 82149012. Its totient is φ = 81318832.

The previous prime is 81733907. The next prime is 81733931. The reversal of 81733921 is 12933718.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 80353296 + 1380625 = 8964^2 + 1175^2 .

It is a cyclic number.

It is not a de Polignac number, because 81733921 - 2⁹ = 81733409 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81733901) 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 in 3 ways as a sum of consecutive naturals, for example, 207250 + ... + 207643.

It is an arithmetic number, because the mean of its divisors is an integer number (20537253).

Almost surely, 2^81733921 is an apocalyptic number.

It is an amenable number.

81733921 is a deficient number, since it is larger than the sum of its proper divisors (415091).

81733921 is a wasteful number, since it uses less digits than its factorization.

81733921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 415090.

The product of its digits is 9072, while the sum is 34.

The square root of 81733921 is about 9040.6814455549. The cubic root of 81733921 is about 433.9777307409.

The spelling of 81733921 in words is "eighty-one million, seven hundred thirty-three thousand, nine hundred twenty-one".