21909287 has 2 divisors, whose sum is σ = 21909288. Its totient is φ = 21909286.

The previous prime is 21909269. The next prime is 21909301. The reversal of 21909287 is 78290912.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21909287 - 2¹⁴ = 21892903 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21909287.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21909227) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10954643 + 10954644.

It is an arithmetic number, because the mean of its divisors is an integer number (10954644).

Almost surely, 2^21909287 is an apocalyptic number.

21909287 is a deficient number, since it is larger than the sum of its proper divisors (1).

21909287 is an equidigital number, since it uses as much as digits as its factorization.

21909287 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 18144, while the sum is 38.

The square root of 21909287 is about 4680.7357327668. The cubic root of 21909287 is about 279.8182791970.

The spelling of 21909287 in words is "twenty-one million, nine hundred nine thousand, two hundred eighty-seven".