78805921 has 2 divisors, whose sum is σ = 78805922. Its totient is φ = 78805920.

The previous prime is 78805907. The next prime is 78805933. The reversal of 78805921 is 12950887.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 78074896 + 731025 = 8836^2 + 855^2 .

It is an emirp because it is prime and its reverse (12950887) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78805921 - 2¹³ = 78797729 is a prime.

It is not a weakly prime, because it can be changed into another prime (78805021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39402960 + 39402961.

It is an arithmetic number, because the mean of its divisors is an integer number (39402961).

Almost surely, 2^78805921 is an apocalyptic number.

It is an amenable number.

78805921 is a deficient number, since it is larger than the sum of its proper divisors (1).

78805921 is an equidigital number, since it uses as much as digits as its factorization.

78805921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40320, while the sum is 40.

The square root of 78805921 is about 8877.2699069027. The cubic root of 78805921 is about 428.7323781882.

The spelling of 78805921 in words is "seventy-eight million, eight hundred five thousand, nine hundred twenty-one".