21654909 has 18 divisors (see below), whose sum is σ = 32406426. Its totient is φ = 13933920.

The previous prime is 21654907. The next prime is 21654931. The reversal of 21654909 is 90945612.

21654909 is a `hidden beast` number, since 2 + 165 + 490 + 9 = 666.

It can be written as a sum of positive squares in 3 ways, for example, as 4040100 + 17614809 = 2010^2 + 4197^2 .

It is not a de Polignac number, because 21654909 - 2¹ = 21654907 is a prime.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21654907) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 6139 + ... + 8999.

It is an arithmetic number, because the mean of its divisors is an integer number (1800357).

Almost surely, 2^21654909 is an apocalyptic number.

21654909 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21654909 is a deficient number, since it is larger than the sum of its proper divisors (10751517).

21654909 is a wasteful number, since it uses less digits than its factorization.

21654909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2925 (or 2893 counting only the distinct ones).

The product of its (nonzero) digits is 19440, while the sum is 36.

The square root of 21654909 is about 4653.4835338701. The cubic root of 21654909 is about 278.7311164455.

The spelling of 21654909 in words is "twenty-one million, six hundred fifty-four thousand, nine hundred nine".