78309865921 has 15 divisors (see below), whose sum is σ = 91372073633. Its totient is φ = 67110988980.

The previous prime is 78309865903. The next prime is 78309865937. The reversal of 78309865921 is 12956890387.

The square root of 78309865921 is 279839.

It is a perfect power (a square), and thus also a powerful number.

It is not a de Polignac number, because 78309865921 - 2¹¹ = 78309863873 is a prime.

It is a super-2 number, since 2×78309865921² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78309865721) by changing a digit.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 13709256 + ... + 13714966.

Almost surely, 2^78309865921 is an apocalyptic number.

78309865921 is the 279839-th square number.

78309865921 is the 139920-th centered octagonal number.

It is an amenable number.

78309865921 is a deficient number, since it is larger than the sum of its proper divisors (13062207712).

78309865921 is an frugal number, since it uses more digits than its factorization.

78309865921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11450 (or 5718 counting only the distinct ones).

The product of its (nonzero) digits is 6531840, while the sum is 58.

The spelling of 78309865921 in words is "seventy-eight billion, three hundred nine million, eight hundred sixty-five thousand, nine hundred twenty-one".