21317729 has 2 divisors, whose sum is σ = 21317730. Its totient is φ = 21317728.

The previous prime is 21317719. The next prime is 21317749. The reversal of 21317729 is 92771312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13337104 + 7980625 = 3652^2 + 2825^2 .

It is a cyclic number.

It is not a de Polignac number, because 21317729 - 2²⁰ = 20269153 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21317695 and 21317704.

It is not a weakly prime, because it can be changed into another prime (21317719) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10658864 + 10658865.

It is an arithmetic number, because the mean of its divisors is an integer number (10658865).

Almost surely, 2^21317729 is an apocalyptic number.

It is an amenable number.

21317729 is a deficient number, since it is larger than the sum of its proper divisors (1).

21317729 is an equidigital number, since it uses as much as digits as its factorization.

21317729 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5292, while the sum is 32.

The square root of 21317729 is about 4617.1126258734. The cubic root of 21317729 is about 277.2768717434.

The spelling of 21317729 in words is "twenty-one million, three hundred seventeen thousand, seven hundred twenty-nine".