81666578 has 16 divisors (see below), whose sum is σ = 141575040. Its totient is φ = 34606176.

The previous prime is 81666551. The next prime is 81666593. The reversal of 81666578 is 87566618.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 31526 + ... + 34017.

It is an arithmetic number, because the mean of its divisors is an integer number (8848440).

Almost surely, 2^81666578 is an apocalyptic number.

81666578 is a deficient number, since it is larger than the sum of its proper divisors (59908462).

81666578 is a wasteful number, since it uses less digits than its factorization.

81666578 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 65641.

The product of its digits is 483840, while the sum is 47.

The square root of 81666578 is about 9036.9562353704. The cubic root of 81666578 is about 433.8585089532.

The spelling of 81666578 in words is "eighty-one million, six hundred sixty-six thousand, five hundred seventy-eight".