21305729 has 2 divisors, whose sum is σ = 21305730. Its totient is φ = 21305728.

The previous prime is 21305719. The next prime is 21305737. The reversal of 21305729 is 92750312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13126129 + 8179600 = 3623^2 + 2860^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21305729 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21305719) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10652864 + 10652865.

It is an arithmetic number, because the mean of its divisors is an integer number (10652865).

Almost surely, 2^21305729 is an apocalyptic number.

It is an amenable number.

21305729 is a deficient number, since it is larger than the sum of its proper divisors (1).

21305729 is an equidigital number, since it uses as much as digits as its factorization.

21305729 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 29.

The square root of 21305729 is about 4615.8129294849. The cubic root of 21305729 is about 277.2248345090.

The spelling of 21305729 in words is "twenty-one million, three hundred five thousand, seven hundred twenty-nine".