81721493 has 8 divisors (see below), whose sum is σ = 95920512. Its totient is φ = 68153616.

The previous prime is 81721481. The next prime is 81721501. The reversal of 81721493 is 39412718.

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 81721493 - 2⁶ = 81721429 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81729493) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 157505 + ... + 158022.

It is an arithmetic number, because the mean of its divisors is an integer number (11990064).

Almost surely, 2^81721493 is an apocalyptic number.

It is an amenable number.

81721493 is a deficient number, since it is larger than the sum of its proper divisors (14199019).

81721493 is a wasteful number, since it uses less digits than its factorization.

81721493 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 315571.

The product of its digits is 12096, while the sum is 35.

The square root of 81721493 is about 9039.9940818565. The cubic root of 81721493 is about 433.9557335556.

The spelling of 81721493 in words is "eighty-one million, seven hundred twenty-one thousand, four hundred ninety-three".