77520721 has 2 divisors, whose sum is σ = 77520722. Its totient is φ = 77520720.

The previous prime is 77520659. The next prime is 77520743. The reversal of 77520721 is 12702577.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 45711121 + 31809600 = 6761^2 + 5640^2 .

It is an emirp because it is prime and its reverse (12702577) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 77520721 - 2¹¹ = 77518673 is a prime.

It is not a weakly prime, because it can be changed into another prime (77580721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 38760360 + 38760361.

It is an arithmetic number, because the mean of its divisors is an integer number (38760361).

Almost surely, 2^77520721 is an apocalyptic number.

It is an amenable number.

77520721 is a deficient number, since it is larger than the sum of its proper divisors (1).

77520721 is an equidigital number, since it uses as much as digits as its factorization.

77520721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6860, while the sum is 31.

The square root of 77520721 is about 8804.5852258922. The cubic root of 77520721 is about 426.3889432750.

The spelling of 77520721 in words is "seventy-seven million, five hundred twenty thousand, seven hundred twenty-one".