81721078 has 4 divisors (see below), whose sum is σ = 122581620. Its totient is φ = 40860538.

The previous prime is 81721051. The next prime is 81721103. The reversal of 81721078 is 87012718.

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

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20430268 + ... + 20430271.

It is an arithmetic number, because the mean of its divisors is an integer number (30645405).

Almost surely, 2^81721078 is an apocalyptic number.

81721078 is a deficient number, since it is larger than the sum of its proper divisors (40860542).

81721078 is a wasteful number, since it uses less digits than its factorization.

81721078 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40860541.

The product of its (nonzero) digits is 6272, while the sum is 34.

The square root of 81721078 is about 9039.9711282725. The cubic root of 81721078 is about 433.9549989796.

The spelling of 81721078 in words is "eighty-one million, seven hundred twenty-one thousand, seventy-eight".