78020721 has 24 divisors (see below), whose sum is σ = 115151400. Its totient is φ = 50893056.

The previous prime is 78020713. The next prime is 78020729. The reversal of 78020721 is 12702087.

It is an interprime number because it is at equal distance from previous prime (78020713) and next prime (78020729).

It can be written as a sum of positive squares in 4 ways, for example, as 3111696 + 74909025 = 1764^2 + 8655^2 .

It is not a de Polignac number, because 78020721 - 2³ = 78020713 is a prime.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78020729) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 97495 + ... + 98291.

It is an arithmetic number, because the mean of its divisors is an integer number (4797975).

Almost surely, 2^78020721 is an apocalyptic number.

It is an amenable number.

78020721 is a deficient number, since it is larger than the sum of its proper divisors (37130679).

78020721 is a wasteful number, since it uses less digits than its factorization.

78020721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1025 (or 1022 counting only the distinct ones).

The product of its (nonzero) digits is 1568, while the sum is 27.

The square root of 78020721 is about 8832.9338840501. The cubic root of 78020721 is about 427.3036997604.

The spelling of 78020721 in words is "seventy-eight million, twenty thousand, seven hundred twenty-one".