81516621 has 4 divisors (see below), whose sum is σ = 108688832. Its totient is φ = 54344412.

The previous prime is 81516607. The next prime is 81516629. The reversal of 81516621 is 12661518.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 81516621 - 2⁷ = 81516493 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 (81516629) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13586101 + ... + 13586106.

It is an arithmetic number, because the mean of its divisors is an integer number (27172208).

Almost surely, 2^81516621 is an apocalyptic number.

It is an amenable number.

81516621 is a deficient number, since it is larger than the sum of its proper divisors (27172211).

81516621 is a wasteful number, since it uses less digits than its factorization.

81516621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27172210.

The product of its digits is 2880, while the sum is 30.

The square root of 81516621 is about 9028.6555477546. The cubic root of 81516621 is about 433.5927944506.

The spelling of 81516621 in words is "eighty-one million, five hundred sixteen thousand, six hundred twenty-one".