766821721 has 2 divisors, whose sum is σ = 766821722. Its totient is φ = 766821720.

The previous prime is 766821719. The next prime is 766821739. The reversal of 766821721 is 127128667.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 675428121 + 91393600 = 25989^2 + 9560^2 .

It is a cyclic number.

It is not a de Polignac number, because 766821721 - 2¹ = 766821719 is a prime.

Together with 766821719, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (766821751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 383410860 + 383410861.

It is an arithmetic number, because the mean of its divisors is an integer number (383410861).

Almost surely, 2^766821721 is an apocalyptic number.

It is an amenable number.

766821721 is a deficient number, since it is larger than the sum of its proper divisors (1).

766821721 is an equidigital number, since it uses as much as digits as its factorization.

766821721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 56448, while the sum is 40.

The square root of 766821721 is about 27691.5460204012. The cubic root of 766821721 is about 915.3028235142.

The spelling of 766821721 in words is "seven hundred sixty-six million, eight hundred twenty-one thousand, seven hundred twenty-one".