7720721621 has 2 divisors, whose sum is σ = 7720721622. Its totient is φ = 7720721620.

The previous prime is 7720721551. The next prime is 7720721641. The reversal of 7720721621 is 1261270277.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 7518797521 + 201924100 = 86711^2 + 14210^2 .

It is a cyclic number.

It is not a de Polignac number, because 7720721621 - 2¹⁸ = 7720459477 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (7720721641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3860360810 + 3860360811.

It is an arithmetic number, because the mean of its divisors is an integer number (3860360811).

Almost surely, 2^7720721621 is an apocalyptic number.

It is an amenable number.

7720721621 is a deficient number, since it is larger than the sum of its proper divisors (1).

7720721621 is an equidigital number, since it uses as much as digits as its factorization.

7720721621 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16464, while the sum is 35.

The square root of 7720721621 is about 87867.6369376120. The cubic root of 7720721621 is about 1976.4506030249.

Adding to 7720721621 its reverse (1261270277), we get a palindrome (8981991898).

The spelling of 7720721621 in words is "seven billion, seven hundred twenty million, seven hundred twenty-one thousand, six hundred twenty-one".