51721309 has 2 divisors, whose sum is σ = 51721310. Its totient is φ = 51721308.

The previous prime is 51721261. The next prime is 51721331. The reversal of 51721309 is 90312715.

51721309 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 47403225 + 4318084 = 6885^2 + 2078^2 .

It is a cyclic number.

It is not a de Polignac number, because 51721309 - 2¹⁵ = 51688541 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (51721399) 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, 25860654 + 25860655.

It is an arithmetic number, because the mean of its divisors is an integer number (25860655).

Almost surely, 2^51721309 is an apocalyptic number.

It is an amenable number.

51721309 is a deficient number, since it is larger than the sum of its proper divisors (1).

51721309 is an equidigital number, since it uses as much as digits as its factorization.

51721309 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1890, while the sum is 28.

The square root of 51721309 is about 7191.7528461426. The cubic root of 51721309 is about 372.5831149459.

The spelling of 51721309 in words is "fifty-one million, seven hundred twenty-one thousand, three hundred nine".