21203729 has 2 divisors, whose sum is σ = 21203730. Its totient is φ = 21203728.

The previous prime is 21203717. The next prime is 21203731. The reversal of 21203729 is 92730212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20720704 + 483025 = 4552^2 + 695^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21203729 is a prime.

Together with 21203731, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21203698 and 21203707.

It is not a weakly prime, because it can be changed into another prime (21203759) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10601864 + 10601865.

It is an arithmetic number, because the mean of its divisors is an integer number (10601865).

Almost surely, 2^21203729 is an apocalyptic number.

It is an amenable number.

21203729 is a deficient number, since it is larger than the sum of its proper divisors (1).

21203729 is an equidigital number, since it uses as much as digits as its factorization.

21203729 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1512, while the sum is 26.

The square root of 21203729 is about 4604.7506990064. The cubic root of 21203729 is about 276.7817271133.

The spelling of 21203729 in words is "twenty-one million, two hundred three thousand, seven hundred twenty-nine".