81555999 has 32 divisors (see below), whose sum is σ = 136519680. Its totient is φ = 42226272.

The previous prime is 81555997. The next prime is 81556001. The reversal of 81555999 is 99955518.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (81555997) and next prime (81556001).

It is not a de Polignac number, because 81555999 - 2¹ = 81555997 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81555997) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4734 + ... + 13620.

It is an arithmetic number, because the mean of its divisors is an integer number (4266240).

Almost surely, 2^81555999 is an apocalyptic number.

81555999 is a deficient number, since it is larger than the sum of its proper divisors (54963681).

81555999 is a wasteful number, since it uses less digits than its factorization.

81555999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8939.

The product of its digits is 729000, while the sum is 51.

The square root of 81555999 is about 9030.8360078123. The cubic root of 81555999 is about 433.6626013533.

The spelling of 81555999 in words is "eighty-one million, five hundred fifty-five thousand, nine hundred ninety-nine".