78854817721 has 3 divisors (see below), whose sum is σ = 78855098533. Its totient is φ = 78854536910.

The previous prime is 78854817703. The next prime is 78854817737. The reversal of 78854817721 is 12771845887.

It is a happy number.

The square root of 78854817721 is 280811.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 78854817721 - 2¹³ = 78854809529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78854877721) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 140406 + ... + 421216.

Almost surely, 2^78854817721 is an apocalyptic number.

78854817721 is the 280811-st square number.

78854817721 is the 140406-th centered octagonal number.

It is an amenable number.

78854817721 is a deficient number, since it is larger than the sum of its proper divisors (280812).

78854817721 is an frugal number, since it uses more digits than its factorization.

78854817721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 561622 (or 280811 counting only the distinct ones).

The product of its digits is 7024640, while the sum is 58.

The spelling of 78854817721 in words is "seventy-eight billion, eight hundred fifty-four million, eight hundred seventeen thousand, seven hundred twenty-one".