21920905 has 8 divisors (see below), whose sum is σ = 27852552. Its totient is φ = 16505088.

The previous prime is 21920903. The next prime is 21920911. The reversal of 21920905 is 50902912.

It can be written as a sum of positive squares in 4 ways, for example, as 2322576 + 19598329 = 1524^2 + 4427^2 .

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 21920905 - 2¹ = 21920903 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21920903) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 128862 + ... + 129031.

It is an arithmetic number, because the mean of its divisors is an integer number (3481569).

Almost surely, 2^21920905 is an apocalyptic number.

It is an amenable number.

21920905 is a deficient number, since it is larger than the sum of its proper divisors (5931647).

21920905 is a wasteful number, since it uses less digits than its factorization.

21920905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 257915.

The product of its (nonzero) digits is 1620, while the sum is 28.

The square root of 21920905 is about 4681.9766125003. The cubic root of 21920905 is about 279.8677308946.

The spelling of 21920905 in words is "twenty-one million, nine hundred twenty thousand, nine hundred five".