81680721 has 16 divisors (see below), whose sum is σ = 111088320. Its totient is φ = 53369280.

The previous prime is 81680701. The next prime is 81680723. The reversal of 81680721 is 12708618.

It is a happy number.

It is not a de Polignac number, because 81680721 - 2⁶ = 81680657 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81680723) 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, 95331 + ... + 96183.

It is an arithmetic number, because the mean of its divisors is an integer number (6943020).

Almost surely, 2^81680721 is an apocalyptic number.

It is an amenable number.

81680721 is a deficient number, since it is larger than the sum of its proper divisors (29407599).

81680721 is a wasteful number, since it uses less digits than its factorization.

81680721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1456.

The product of its (nonzero) digits is 5376, while the sum is 33.

The square root of 81680721 is about 9037.7387105404. The cubic root of 81680721 is about 433.8835526812.

The spelling of 81680721 in words is "eighty-one million, six hundred eighty thousand, seven hundred twenty-one".