81721871 has 8 divisors (see below), whose sum is σ = 101887104. Its totient is φ = 63679320.

The previous prime is 81721867. The next prime is 81721877. The reversal of 81721871 is 17812718.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81721871 - 2² = 81721867 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81721877) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 530585 + ... + 530738.

It is an arithmetic number, because the mean of its divisors is an integer number (12735888).

Almost surely, 2^81721871 is an apocalyptic number.

81721871 is a deficient number, since it is larger than the sum of its proper divisors (20165233).

81721871 is a wasteful number, since it uses less digits than its factorization.

81721871 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1061341.

The product of its digits is 6272, while the sum is 35.

The square root of 81721871 is about 9040.0149889256. The cubic root of 81721871 is about 433.9564026371.

The spelling of 81721871 in words is "eighty-one million, seven hundred twenty-one thousand, eight hundred seventy-one".