21251905 has 8 divisors (see below), whose sum is σ = 25529472. Its totient is φ = 16983408.

The previous prime is 21251903. The next prime is 21251929. The reversal of 21251905 is 50915212.

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 21251905 - 2¹ = 21251903 is a prime.

It is a super-2 number, since 2×21251905² = 903286932258050, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21251905.

It is not an unprimeable number, because it can be changed into a prime (21251903) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5034 + ... + 8236.

It is an arithmetic number, because the mean of its divisors is an integer number (3191184).

Almost surely, 2^21251905 is an apocalyptic number.

It is an amenable number.

21251905 is a deficient number, since it is larger than the sum of its proper divisors (4277567).

21251905 is a wasteful number, since it uses less digits than its factorization.

21251905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4535.

The product of its (nonzero) digits is 900, while the sum is 25.

The square root of 21251905 is about 4609.9788502769. The cubic root of 21251905 is about 276.9911894916.

The spelling of 21251905 in words is "twenty-one million, two hundred fifty-one thousand, nine hundred five".