78805721 has 4 divisors (see below), whose sum is σ = 78838452. Its totient is φ = 78772992.

The previous prime is 78805703. The next prime is 78805729. The reversal of 78805721 is 12750887.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12750887 = 139 ⋅91733.

It can be written as a sum of positive squares in 2 ways, for example, as 75342400 + 3463321 = 8680^2 + 1861^2 .

It is a cyclic number.

It is not a de Polignac number, because 78805721 - 2²² = 74611417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78805729) 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, 12440 + ... + 17673.

It is an arithmetic number, because the mean of its divisors is an integer number (19709613).

Almost surely, 2^78805721 is an apocalyptic number.

It is an amenable number.

78805721 is a deficient number, since it is larger than the sum of its proper divisors (32731).

78805721 is a wasteful number, since it uses less digits than its factorization.

78805721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32730.

The product of its (nonzero) digits is 31360, while the sum is 38.

The square root of 78805721 is about 8877.2586421710. The cubic root of 78805721 is about 428.7320154974.

The spelling of 78805721 in words is "seventy-eight million, eight hundred five thousand, seven hundred twenty-one".