77721920 has 56 divisors (see below), whose sum is σ = 187223400. Its totient is φ = 30728192.

The previous prime is 77721893. The next prime is 77721923. The reversal of 77721920 is 2912777.

It can be written as a sum of positive squares in 4 ways, for example, as 14868736 + 62853184 = 3856^2 + 7928^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (77721923) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 27116 + ... + 29844.

It is an arithmetic number, because the mean of its divisors is an integer number (3343275).

Almost surely, 2^77721920 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 77721920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (93611700).

77721920 is an abundant number, since it is smaller than the sum of its proper divisors (109501480).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

77721920 is a wasteful number, since it uses less digits than its factorization.

77721920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2835 (or 2825 counting only the distinct ones).

The product of its (nonzero) digits is 12348, while the sum is 35.

The square root of 77721920 is about 8816.0036297633. The cubic root of 77721920 is about 426.7575110383.

The spelling of 77721920 in words is "seventy-seven million, seven hundred twenty-one thousand, nine hundred twenty".