21854509 has 4 divisors (see below), whose sum is σ = 21939804. Its totient is φ = 21769216.

The previous prime is 21854507. The next prime is 21854527. The reversal of 21854509 is 90545812.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 16080100 + 5774409 = 4010^2 + 2403^2 .

It is a cyclic number.

It is not a de Polignac number, because 21854509 - 2¹ = 21854507 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21854501) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 42262 + ... + 42775.

It is an arithmetic number, because the mean of its divisors is an integer number (5484951).

Almost surely, 2^21854509 is an apocalyptic number.

It is an amenable number.

21854509 is a deficient number, since it is larger than the sum of its proper divisors (85295).

21854509 is an equidigital number, since it uses as much as digits as its factorization.

21854509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 85294.

The product of its (nonzero) digits is 14400, while the sum is 34.

The square root of 21854509 is about 4674.8806401875. The cubic root of 21854509 is about 279.5848823149.

The spelling of 21854509 in words is "twenty-one million, eight hundred fifty-four thousand, five hundred nine".