21809087 has 2 divisors, whose sum is σ = 21809088. Its totient is φ = 21809086.

The previous prime is 21809071. The next prime is 21809101. The reversal of 21809087 is 78090812.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21809087 - 2⁴ = 21809071 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21809057) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10904543 + 10904544.

It is an arithmetic number, because the mean of its divisors is an integer number (10904544).

Almost surely, 2^21809087 is an apocalyptic number.

21809087 is a deficient number, since it is larger than the sum of its proper divisors (1).

21809087 is an equidigital number, since it uses as much as digits as its factorization.

21809087 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8064, while the sum is 35.

The square root of 21809087 is about 4670.0200213704. The cubic root of 21809087 is about 279.3910533177.

Adding to 21809087 its reverse (78090812), we get a palindrome (99899899).

The spelling of 21809087 in words is "twenty-one million, eight hundred nine thousand, eighty-seven".