81438721 has 32 divisors (see below), whose sum is σ = 107993088. Its totient is φ = 59581440.

The previous prime is 81438683. The next prime is 81438787. The reversal of 81438721 is 12783418.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 81438721 - 2⁷ = 81438593 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (81430721) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 93936 + ... + 94798.

It is an arithmetic number, because the mean of its divisors is an integer number (3374784).

Almost surely, 2^81438721 is an apocalyptic number.

It is an amenable number.

81438721 is a deficient number, since it is larger than the sum of its proper divisors (26554367).

81438721 is a wasteful number, since it uses less digits than its factorization.

81438721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 961.

The product of its digits is 10752, while the sum is 34.

The square root of 81438721 is about 9024.3404745167. The cubic root of 81438721 is about 433.4546318550.

The spelling of 81438721 in words is "eighty-one million, four hundred thirty-eight thousand, seven hundred twenty-one".