81729866 has 4 divisors (see below), whose sum is σ = 122594802. Its totient is φ = 40864932.

The previous prime is 81729841. The next prime is 81729881. The reversal of 81729866 is 66892718.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 81522841 + 207025 = 9029^2 + 455^2 .

It is a super-3 number, since 3×81729866³ (a number of 25 digits) contains 333 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 81729866.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20432465 + ... + 20432468.

Almost surely, 2^81729866 is an apocalyptic number.

81729866 is a deficient number, since it is larger than the sum of its proper divisors (40864936).

81729866 is a wasteful number, since it uses less digits than its factorization.

81729866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40864935.

The product of its digits is 290304, while the sum is 47.

The square root of 81729866 is about 9040.4571787051. The cubic root of 81729866 is about 433.9705537583.

The spelling of 81729866 in words is "eighty-one million, seven hundred twenty-nine thousand, eight hundred sixty-six".