21384991 has 2 divisors, whose sum is σ = 21384992. Its totient is φ = 21384990.

The previous prime is 21384983. The next prime is 21385057. The reversal of 21384991 is 19948312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21384991 - 2³ = 21384983 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21384991.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21384931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10692495 + 10692496.

It is an arithmetic number, because the mean of its divisors is an integer number (10692496).

Almost surely, 2^21384991 is an apocalyptic number.

21384991 is a deficient number, since it is larger than the sum of its proper divisors (1).

21384991 is an equidigital number, since it uses as much as digits as its factorization.

21384991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 37.

The square root of 21384991 is about 4624.3908788077. The cubic root of 21384991 is about 277.5681882049.

The spelling of 21384991 in words is "twenty-one million, three hundred eighty-four thousand, nine hundred ninety-one".