21865290 has 16 divisors (see below), whose sum is σ = 52476768. Its totient is φ = 5830736.

The previous prime is 21865289. The next prime is 21865331. The reversal of 21865290 is 9256812.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 364392 + ... + 364451.

It is an arithmetic number, because the mean of its divisors is an integer number (3279798).

Almost surely, 2^21865290 is an apocalyptic number.

21865290 is an abundant number, since it is smaller than the sum of its proper divisors (30611478).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21865290 is a wasteful number, since it uses less digits than its factorization.

21865290 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 728853.

The product of its (nonzero) digits is 8640, while the sum is 33.

The square root of 21865290 is about 4676.0335755852. The cubic root of 21865290 is about 279.6308485594.

It can be divided in two parts, 21865 and 290, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 21865290 in words is "twenty-one million, eight hundred sixty-five thousand, two hundred ninety".