78500021 has 2 divisors, whose sum is σ = 78500022. Its totient is φ = 78500020.

The previous prime is 78500003. The next prime is 78500027. The reversal of 78500021 is 12000587.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 78127921 + 372100 = 8839^2 + 610^2 .

It is an emirp because it is prime and its reverse (12000587) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78500021 - 2²² = 74305717 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 78500021.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78500027) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39250010 + 39250011.

It is an arithmetic number, because the mean of its divisors is an integer number (39250011).

Almost surely, 2^78500021 is an apocalyptic number.

It is an amenable number.

78500021 is a deficient number, since it is larger than the sum of its proper divisors (1).

78500021 is an equidigital number, since it uses as much as digits as its factorization.

78500021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 560, while the sum is 23.

The square root of 78500021 is about 8860.0237584332. The cubic root of 78500021 is about 428.1769237537.

The spelling of 78500021 in words is "seventy-eight million, five hundred thousand, twenty-one".