78215821 has 8 divisors (see below), whose sum is σ = 80939264. Its totient is φ = 75504960.

The previous prime is 78215791. The next prime is 78215833. The reversal of 78215821 is 12851287.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 78215821 - 2⁵ = 78215789 is a prime.

It is a super-2 number, since 2×78215821² = 12235429309408082, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78215881) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10510 + ... + 16336.

It is an arithmetic number, because the mean of its divisors is an integer number (10117408).

Almost surely, 2^78215821 is an apocalyptic number.

It is an amenable number.

78215821 is a deficient number, since it is larger than the sum of its proper divisors (2723443).

78215821 is a wasteful number, since it uses less digits than its factorization.

78215821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6291.

The product of its digits is 8960, while the sum is 34.

The square root of 78215821 is about 8843.9708841674. The cubic root of 78215821 is about 427.6595776926.

The spelling of 78215821 in words is "seventy-eight million, two hundred fifteen thousand, eight hundred twenty-one".