78821857 has 4 divisors (see below), whose sum is σ = 79932096. Its totient is φ = 77711620.

The previous prime is 78821839. The next prime is 78821879. The reversal of 78821857 is 75812887.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 75812887 = 31 ⋅2445577.

It is a cyclic number.

It is not a de Polignac number, because 78821857 - 2²³ = 70433249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78821807) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 555013 + ... + 555154.

It is an arithmetic number, because the mean of its divisors is an integer number (19983024).

Almost surely, 2^78821857 is an apocalyptic number.

It is an amenable number.

78821857 is a deficient number, since it is larger than the sum of its proper divisors (1110239).

78821857 is a wasteful number, since it uses less digits than its factorization.

78821857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1110238.

The product of its digits is 250880, while the sum is 46.

The square root of 78821857 is about 8878.1674347807. The cubic root of 78821857 is about 428.7612754191.

The spelling of 78821857 in words is "seventy-eight million, eight hundred twenty-one thousand, eight hundred fifty-seven".