21549905 has 8 divisors (see below), whose sum is σ = 27849192. Its totient is φ = 15913728.

The previous prime is 21549901. The next prime is 21549911. The reversal of 21549905 is 50994512.

It can be written as a sum of positive squares in 4 ways, for example, as 29584 + 21520321 = 172^2 + 4639^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21549905 - 2² = 21549901 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21549901) 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 in 7 ways as a sum of consecutive naturals, for example, 165704 + ... + 165833.

It is an arithmetic number, because the mean of its divisors is an integer number (3481149).

Almost surely, 2^21549905 is an apocalyptic number.

It is an amenable number.

21549905 is a deficient number, since it is larger than the sum of its proper divisors (6299287).

21549905 is a wasteful number, since it uses less digits than its factorization.

21549905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 331555.

The product of its (nonzero) digits is 16200, while the sum is 35.

The square root of 21549905 is about 4642.1875231404. The cubic root of 21549905 is about 278.2798667026.

The spelling of 21549905 in words is "twenty-one million, five hundred forty-nine thousand, nine hundred five".