21391259 has 2 divisors, whose sum is σ = 21391260. Its totient is φ = 21391258.

The previous prime is 21391213. The next prime is 21391261. The reversal of 21391259 is 95219312.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21391259 is a prime.

Together with 21391261, it forms a pair of twin primes.

It is a Chen prime.

It is a plaindrome in base 16.

It is not a weakly prime, because it can be changed into another prime (21361259) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10695629 + 10695630.

It is an arithmetic number, because the mean of its divisors is an integer number (10695630).

Almost surely, 2^21391259 is an apocalyptic number.

21391259 is a deficient number, since it is larger than the sum of its proper divisors (1).

21391259 is an equidigital number, since it uses as much as digits as its factorization.

21391259 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4860, while the sum is 32.

The square root of 21391259 is about 4625.0685400327. The cubic root of 21391259 is about 277.5953042237.

The spelling of 21391259 in words is "twenty-one million, three hundred ninety-one thousand, two hundred fifty-nine".