21212591 has 2 divisors, whose sum is σ = 21212592. Its totient is φ = 21212590.

The previous prime is 21212537. The next prime is 21212593. The reversal of 21212591 is 19521212.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21212591 is a prime.

Together with 21212593, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21212593) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606295 + 10606296.

It is an arithmetic number, because the mean of its divisors is an integer number (10606296).

Almost surely, 2^21212591 is an apocalyptic number.

21212591 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212591 is an equidigital number, since it uses as much as digits as its factorization.

21212591 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 360, while the sum is 23.

The square root of 21212591 is about 4605.7128655616. The cubic root of 21212591 is about 276.8202816214.

The spelling of 21212591 in words is "twenty-one million, two hundred twelve thousand, five hundred ninety-one".