81230721 has 16 divisors (see below), whose sum is σ = 127243200. Its totient is φ = 45443520.

The previous prime is 81230707. The next prime is 81230729. The reversal of 81230721 is 12703218.

It is not a de Polignac number, because 81230721 - 2⁹ = 81230209 is a prime.

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

It is a junction number, because it is equal to n+sod(n) for n = 81230691 and 81230700.

It is not an unprimeable number, because it can be changed into a prime (81230729) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 94246 + ... + 95103.

It is an arithmetic number, because the mean of its divisors is an integer number (7952700).

Almost surely, 2^81230721 is an apocalyptic number.

It is an amenable number.

81230721 is a deficient number, since it is larger than the sum of its proper divisors (46012479).

81230721 is a wasteful number, since it uses less digits than its factorization.

81230721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 189376.

The product of its (nonzero) digits is 672, while the sum is 24.

The square root of 81230721 is about 9012.8087187069. The cubic root of 81230721 is about 433.0852930915.

Adding to 81230721 its reverse (12703218), we get a palindrome (93933939).

The spelling of 81230721 in words is "eighty-one million, two hundred thirty thousand, seven hundred twenty-one".