81721515 has 8 divisors (see below), whose sum is σ = 130754448. Its totient is φ = 43584800.

The previous prime is 81721513. The next prime is 81721531. The reversal of 81721515 is 51512718.

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

It is not a de Polignac number, because 81721515 - 2¹ = 81721513 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81721511) 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, 2724036 + ... + 2724065.

It is an arithmetic number, because the mean of its divisors is an integer number (16344306).

Almost surely, 2^81721515 is an apocalyptic number.

81721515 is a deficient number, since it is larger than the sum of its proper divisors (49032933).

81721515 is a wasteful number, since it uses less digits than its factorization.

81721515 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5448109.

The product of its digits is 2800, while the sum is 30.

The square root of 81721515 is about 9039.9952986713. The cubic root of 81721515 is about 433.9557724969.

The spelling of 81721515 in words is "eighty-one million, seven hundred twenty-one thousand, five hundred fifteen".