21204891 has 24 divisors (see below), whose sum is σ = 31631600. Its totient is φ = 13680576.

The previous prime is 21204889. The next prime is 21204917. The reversal of 21204891 is 19840212.

It is not a de Polignac number, because 21204891 - 2¹ = 21204889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21204871) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 60585 + ... + 60933.

Almost surely, 2^21204891 is an apocalyptic number.

21204891 is a deficient number, since it is larger than the sum of its proper divisors (10426709).

21204891 is a wasteful number, since it uses less digits than its factorization.

21204891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 555 (or 552 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 27.

The square root of 21204891 is about 4604.8768713181. The cubic root of 21204891 is about 276.7867830556.

It can be divided in two parts, 21 and 204891, that multiplied together give a triangular number (4302711 = T₂₉₃₃).

The spelling of 21204891 in words is "twenty-one million, two hundred four thousand, eight hundred ninety-one".