721669691 has 2 divisors, whose sum is σ = 721669692. Its totient is φ = 721669690.

The previous prime is 721669687. The next prime is 721669709. The reversal of 721669691 is 196966127.

It is a weak prime.

It is an emirp because it is prime and its reverse (196966127) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 721669691 - 2² = 721669687 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (721669891) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360834845 + 360834846.

It is an arithmetic number, because the mean of its divisors is an integer number (360834846).

Almost surely, 2^721669691 is an apocalyptic number.

721669691 is a deficient number, since it is larger than the sum of its proper divisors (1).

721669691 is an equidigital number, since it uses as much as digits as its factorization.

721669691 is an evil number, because the sum of its binary digits is even.

The product of its digits is 244944, while the sum is 47.

The square root of 721669691 is about 26863.9105678976. The cubic root of 721669691 is about 896.9732441776.

The spelling of 721669691 in words is "seven hundred twenty-one million, six hundred sixty-nine thousand, six hundred ninety-one".