78215709 has 32 divisors (see below), whose sum is σ = 127862784. Its totient is φ = 41849280.

The previous prime is 78215707. The next prime is 78215719. The reversal of 78215709 is 90751287.

It is not a de Polignac number, because 78215709 - 2¹ = 78215707 is a prime.

It is a super-2 number, since 2×78215709² = 12235394268745362, which contains 22 as substring.

It is a Smith number, since the sum of its digits (39) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78215701) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5904 + ... + 13830.

It is an arithmetic number, because the mean of its divisors is an integer number (3995712).

Almost surely, 2^78215709 is an apocalyptic number.

It is an amenable number.

78215709 is a deficient number, since it is larger than the sum of its proper divisors (49647075).

78215709 is a wasteful number, since it uses less digits than its factorization.

78215709 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7977.

The product of its (nonzero) digits is 35280, while the sum is 39.

The square root of 78215709 is about 8843.9645521678. The cubic root of 78215709 is about 427.6593735655.

It can be divided in two parts, 7821 and 5709, that added together give a triangular number (13530 = T₁₆₄).

The spelling of 78215709 in words is "seventy-eight million, two hundred fifteen thousand, seven hundred nine".