81921811 has 4 divisors (see below), whose sum is σ = 84135952. Its totient is φ = 79707672.

The previous prime is 81921797. The next prime is 81921857. The reversal of 81921811 is 11812918.

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

It is a cyclic number.

It is not a de Polignac number, because 81921811 - 2⁵ = 81921779 is a prime.

It is a super-2 number, since 2×81921811² = 13422366235039442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81921881) 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, 1107015 + ... + 1107088.

It is an arithmetic number, because the mean of its divisors is an integer number (21033988).

Almost surely, 2^81921811 is an apocalyptic number.

81921811 is a deficient number, since it is larger than the sum of its proper divisors (2214141).

81921811 is a wasteful number, since it uses less digits than its factorization.

81921811 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2214140.

The product of its digits is 1152, while the sum is 31.

The square root of 81921811 is about 9051.0668431959. The cubic root of 81921811 is about 434.3100190289.

The spelling of 81921811 in words is "eighty-one million, nine hundred twenty-one thousand, eight hundred eleven".