78561821 has 4 divisors (see below), whose sum is σ = 84605052. Its totient is φ = 72518592.

The previous prime is 78561803. The next prime is 78561823. The reversal of 78561821 is 12816587.

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

It can be written as a sum of positive squares in 2 ways, for example, as 24700900 + 53860921 = 4970^2 + 7339^2 .

It is a cyclic number.

It is not a de Polignac number, because 78561821 - 2⁶ = 78561757 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (78561823) 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, 3021596 + ... + 3021621.

It is an arithmetic number, because the mean of its divisors is an integer number (21151263).

Almost surely, 2^78561821 is an apocalyptic number.

It is an amenable number.

78561821 is a deficient number, since it is larger than the sum of its proper divisors (6043231).

78561821 is a wasteful number, since it uses less digits than its factorization.

78561821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6043230.

The product of its digits is 26880, while the sum is 38.

The square root of 78561821 is about 8863.5106475933. The cubic root of 78561821 is about 428.2892566023.

The spelling of 78561821 in words is "seventy-eight million, five hundred sixty-one thousand, eight hundred twenty-one".