21055399 has 2 divisors, whose sum is σ = 21055400. Its totient is φ = 21055398.

The previous prime is 21055387. The next prime is 21055409. The reversal of 21055399 is 99355012.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21055399 - 2¹⁷ = 20924327 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21055319) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10527699 + 10527700.

It is an arithmetic number, because the mean of its divisors is an integer number (10527700).

Almost surely, 2^21055399 is an apocalyptic number.

21055399 is a deficient number, since it is larger than the sum of its proper divisors (1).

21055399 is an equidigital number, since it uses as much as digits as its factorization.

21055399 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12150, while the sum is 34.

The square root of 21055399 is about 4588.6162402188. The cubic root of 21055399 is about 276.1348103935.

The spelling of 21055399 in words is "twenty-one million, fifty-five thousand, three hundred ninety-nine".