81621759 has 4 divisors (see below), whose sum is σ = 108829016. Its totient is φ = 54414504.

The previous prime is 81621731. The next prime is 81621767. The reversal of 81621759 is 95712618.

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

It is not a de Polignac number, because 81621759 - 2⁹ = 81621247 is a prime.

It is a super-2 number, since 2×81621759² = 13324223084508162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81621259) by changing a digit.

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 in 3 ways as a sum of consecutive naturals, for example, 13603624 + ... + 13603629.

It is an arithmetic number, because the mean of its divisors is an integer number (27207254).

Almost surely, 2^81621759 is an apocalyptic number.

81621759 is a deficient number, since it is larger than the sum of its proper divisors (27207257).

81621759 is a wasteful number, since it uses less digits than its factorization.

81621759 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27207256.

The product of its digits is 30240, while the sum is 39.

The square root of 81621759 is about 9034.4761331247. The cubic root of 81621759 is about 433.7791265699.

The spelling of 81621759 in words is "eighty-one million, six hundred twenty-one thousand, seven hundred fifty-nine".