78257821 has 2 divisors, whose sum is σ = 78257822. Its totient is φ = 78257820.

The previous prime is 78257819. The next prime is 78257873. The reversal of 78257821 is 12875287.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 77633721 + 624100 = 8811^2 + 790^2 .

It is an emirp because it is prime and its reverse (12875287) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 78257821 - 2¹ = 78257819 is a prime.

It is a super-2 number, since 2×78257821² = 12248573095336082, which contains 22 as substring.

Together with 78257819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (78257801) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 39128910 + 39128911.

It is an arithmetic number, because the mean of its divisors is an integer number (39128911).

Almost surely, 2^78257821 is an apocalyptic number.

It is an amenable number.

78257821 is a deficient number, since it is larger than the sum of its proper divisors (1).

78257821 is an equidigital number, since it uses as much as digits as its factorization.

78257821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 62720, while the sum is 40.

The square root of 78257821 is about 8846.3450644885. The cubic root of 78257821 is about 427.7361116043.

The spelling of 78257821 in words is "seventy-eight million, two hundred fifty-seven thousand, eight hundred twenty-one".