77721220 has 12 divisors (see below), whose sum is σ = 163214604. Its totient is φ = 31088480.

The previous prime is 77721211. The next prime is 77721223. The reversal of 77721220 is 2212777.

It can be written as a sum of positive squares in 2 ways, for example, as 32239684 + 45481536 = 5678^2 + 6744^2 .

It is not an unprimeable number, because it can be changed into a prime (77721223) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1943011 + ... + 1943050.

It is an arithmetic number, because the mean of its divisors is an integer number (13601217).

Almost surely, 2^77721220 is an apocalyptic number.

It is an amenable number.

77721220 is an abundant number, since it is smaller than the sum of its proper divisors (85493384).

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

77721220 is a wasteful number, since it uses less digits than its factorization.

77721220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3886070 (or 3886068 counting only the distinct ones).

The product of its (nonzero) digits is 2744, while the sum is 28.

The square root of 77721220 is about 8815.9639291458. The cubic root of 77721220 is about 426.7562298418.

Adding to 77721220 its reverse (2212777), we get a palindrome (79933997).

The spelling of 77721220 in words is "seventy-seven million, seven hundred twenty-one thousand, two hundred twenty".