81639899 has 24 divisors (see below), whose sum is σ = 96388176. Its totient is φ = 68544000.

The previous prime is 81639889. The next prime is 81639907. The reversal of 81639899 is 99893618.

It is not a de Polignac number, because 81639899 - 2²⁴ = 64862683 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81639899.

It is not an unprimeable number, because it can be changed into a prime (81639809) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 193709 + ... + 194129.

It is an arithmetic number, because the mean of its divisors is an integer number (4016174).

Almost surely, 2^81639899 is an apocalyptic number.

81639899 is a deficient number, since it is larger than the sum of its proper divisors (14748277).

81639899 is a wasteful number, since it uses less digits than its factorization.

81639899 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 527 (or 510 counting only the distinct ones).

The product of its digits is 839808, while the sum is 53.

The square root of 81639899 is about 9035.4800093852. The cubic root of 81639899 is about 433.8112592210.

The spelling of 81639899 in words is "eighty-one million, six hundred thirty-nine thousand, eight hundred ninety-nine".