721615009 has 2 divisors, whose sum is σ = 721615010. Its totient is φ = 721615008.

The previous prime is 721615007. The next prime is 721615019. The reversal of 721615009 is 900516127.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 633780625 + 87834384 = 25175^2 + 9372^2 .

It is a cyclic number.

It is not a de Polignac number, because 721615009 - 2¹ = 721615007 is a prime.

Together with 721615007, it forms a pair of twin primes.

It is equal to p_37313329 and since 721615009 and 37313329 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (721615007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 360807504 + 360807505.

It is an arithmetic number, because the mean of its divisors is an integer number (360807505).

Almost surely, 2^721615009 is an apocalyptic number.

It is an amenable number.

721615009 is a deficient number, since it is larger than the sum of its proper divisors (1).

721615009 is an equidigital number, since it uses as much as digits as its factorization.

721615009 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3780, while the sum is 31.

The square root of 721615009 is about 26862.8927891246. The cubic root of 721615009 is about 896.9505886006.

The spelling of 721615009 in words is "seven hundred twenty-one million, six hundred fifteen thousand, nine".