21009743 has 2 divisors, whose sum is σ = 21009744. Its totient is φ = 21009742.

The previous prime is 21009733. The next prime is 21009749. The reversal of 21009743 is 34790012.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21009743 - 2⁶ = 21009679 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21009749) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10504871 + 10504872.

It is an arithmetic number, because the mean of its divisors is an integer number (10504872).

Almost surely, 2^21009743 is an apocalyptic number.

21009743 is a deficient number, since it is larger than the sum of its proper divisors (1).

21009743 is an equidigital number, since it uses as much as digits as its factorization.

21009743 is an odious number, because the sum of its binary digits is odd.

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

The square root of 21009743 is about 4583.6386201358. The cubic root of 21009743 is about 275.9350780227.

Adding to 21009743 its reverse (34790012), we get a palindrome (55799755).

The spelling of 21009743 in words is "twenty-one million, nine thousand, seven hundred forty-three".