81969891 has 8 divisors (see below), whose sum is σ = 109843200. Its totient is φ = 54371592.

The previous prime is 81969871. The next prime is 81969917. The reversal of 81969891 is 19896918.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81969891 - 2²³ = 73581283 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81969841) 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 7 ways as a sum of consecutive naturals, for example, 68055 + ... + 69248.

It is an arithmetic number, because the mean of its divisors is an integer number (13730400).

Almost surely, 2^81969891 is an apocalyptic number.

81969891 is a deficient number, since it is larger than the sum of its proper divisors (27873309).

81969891 is a wasteful number, since it uses less digits than its factorization.

81969891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 137505.

The product of its digits is 279936, while the sum is 51.

The square root of 81969891 is about 9053.7224940905. The cubic root of 81969891 is about 434.3949680864.

The spelling of 81969891 in words is "eighty-one million, nine hundred sixty-nine thousand, eight hundred ninety-one".