77961985921 has 4 divisors (see below), whose sum is σ = 78251807700. Its totient is φ = 77672164144.

The previous prime is 77961985919. The next prime is 77961985931. The reversal of 77961985921 is 12958916977.

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 2315534400 + 75646451521 = 48120^2 + 275039^2 .

It is a cyclic number.

It is not a de Polignac number, because 77961985921 - 2¹ = 77961985919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (77961985931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 144910486 + ... + 144911023.

It is an arithmetic number, because the mean of its divisors is an integer number (19562951925).

Almost surely, 2^77961985921 is an apocalyptic number.

It is an amenable number.

77961985921 is a deficient number, since it is larger than the sum of its proper divisors (289821779).

77961985921 is a wasteful number, since it uses less digits than its factorization.

77961985921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 289821778.

The product of its digits is 17146080, while the sum is 64.

The spelling of 77961985921 in words is "seventy-seven billion, nine hundred sixty-one million, nine hundred eighty-five thousand, nine hundred twenty-one".