21557099 has 2 divisors, whose sum is σ = 21557100. Its totient is φ = 21557098.

The previous prime is 21557057. The next prime is 21557101. The reversal of 21557099 is 99075512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21557099 - 2¹⁶ = 21491563 is a prime.

It is a Sophie Germain prime.

Together with 21557101, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21550099) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778549 + 10778550.

It is an arithmetic number, because the mean of its divisors is an integer number (10778550).

Almost surely, 2^21557099 is an apocalyptic number.

21557099 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557099 is an equidigital number, since it uses as much as digits as its factorization.

21557099 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 28350, while the sum is 38.

The square root of 21557099 is about 4642.9623086990. The cubic root of 21557099 is about 278.3108292928.

The spelling of 21557099 in words is "twenty-one million, five hundred fifty-seven thousand, ninety-nine".