78561923521 has 9 divisors (see below), whose sum is σ = 79221287649. Its totient is φ = 77908009284.

The previous prime is 78561923497. The next prime is 78561923537. The reversal of 78561923521 is 12532916587.

The square root of 78561923521 is 280289.

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

It is not a de Polignac number, because 78561923521 - 2¹⁵ = 78561890753 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (78561923021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 35595600 + ... + 35597806.

Almost surely, 2^78561923521 is an apocalyptic number.

78561923521 is the 280289-th square number.

78561923521 is the 140145-th centered octagonal number.

It is an amenable number.

78561923521 is a deficient number, since it is larger than the sum of its proper divisors (659364128).

78561923521 is an frugal number, since it uses more digits than its factorization.

78561923521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4668 (or 2334 counting only the distinct ones).

The product of its digits is 907200, while the sum is 49.

Multiplying 78561923521 by its sum of digits (49), we get a square (3849534252529 = 1962023²).

The spelling of 78561923521 in words is "seventy-eight billion, five hundred sixty-one million, nine hundred twenty-three thousand, five hundred twenty-one".