81666999 has 6 divisors (see below), whose sum is σ = 117963456. Its totient is φ = 54444660.

The previous prime is 81666979. The next prime is 81667007. The reversal of 81666999 is 99966618.

It is not a de Polignac number, because 81666999 - 2⁵ = 81666967 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81666979) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4537047 + ... + 4537064.

It is an arithmetic number, because the mean of its divisors is an integer number (19660576).

Almost surely, 2^81666999 is an apocalyptic number.

81666999 is a deficient number, since it is larger than the sum of its proper divisors (36296457).

81666999 is a wasteful number, since it uses less digits than its factorization.

81666999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9074117 (or 9074114 counting only the distinct ones).

The product of its digits is 1259712, while the sum is 54.

The square root of 81666999 is about 9036.9795285814. The cubic root of 81666999 is about 433.8592544810.

The spelling of 81666999 in words is "eighty-one million, six hundred sixty-six thousand, nine hundred ninety-nine".