78605721 has 10 divisors (see below), whose sum is σ = 117423482. Its totient is φ = 52403760.

The previous prime is 78605707. The next prime is 78605741. The reversal of 78605721 is 12750687.

78605721 is a `hidden beast` number, since 7 + 86 + 0 + 572 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 74649600 + 3956121 = 8640^2 + 1989^2 .

It is not a de Polignac number, because 78605721 - 2¹³ = 78597529 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (78605741) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 485140 + ... + 485301.

Almost surely, 2^78605721 is an apocalyptic number.

It is an amenable number.

78605721 is a deficient number, since it is larger than the sum of its proper divisors (38817761).

78605721 is an equidigital number, since it uses as much as digits as its factorization.

78605721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 970453 (or 970444 counting only the distinct ones).

The product of its (nonzero) digits is 23520, while the sum is 36.

The square root of 78605721 is about 8865.9867471139. The cubic root of 78605721 is about 428.3690171318.

The spelling of 78605721 in words is "seventy-eight million, six hundred five thousand, seven hundred twenty-one".