21204487 has 2 divisors, whose sum is σ = 21204488. Its totient is φ = 21204486.

The previous prime is 21204451. The next prime is 21204493. The reversal of 21204487 is 78440212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21204487 - 2¹⁹ = 20680199 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21204497) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10602243 + 10602244.

It is an arithmetic number, because the mean of its divisors is an integer number (10602244).

Almost surely, 2^21204487 is an apocalyptic number.

21204487 is a deficient number, since it is larger than the sum of its proper divisors (1).

21204487 is an equidigital number, since it uses as much as digits as its factorization.

21204487 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3584, while the sum is 28.

The square root of 21204487 is about 4604.8330045725. The cubic root of 21204487 is about 276.7850252446.

Adding to 21204487 its reverse (78440212), we get a palindrome (99644699).

The spelling of 21204487 in words is "twenty-one million, two hundred four thousand, four hundred eighty-seven".