78521399 has 4 divisors (see below), whose sum is σ = 85659720. Its totient is φ = 71383080.

The previous prime is 78521383. The next prime is 78521411. The reversal of 78521399 is 99312587.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 78521399 - 2⁴ = 78521383 is a prime.

It is a super-2 number, since 2×78521399² = 12331220201834402, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78521309) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3569144 + ... + 3569165.

It is an arithmetic number, because the mean of its divisors is an integer number (21414930).

Almost surely, 2^78521399 is an apocalyptic number.

78521399 is a deficient number, since it is larger than the sum of its proper divisors (7138321).

78521399 is a wasteful number, since it uses less digits than its factorization.

78521399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7138320.

The product of its digits is 136080, while the sum is 44.

The square root of 78521399 is about 8861.2301064807. The cubic root of 78521399 is about 428.2157888620.

The spelling of 78521399 in words is "seventy-eight million, five hundred twenty-one thousand, three hundred ninety-nine".