21651905 has 8 divisors (see below), whose sum is σ = 28344384. Its totient is φ = 15746800.

The previous prime is 21651881. The next prime is 21651907. The reversal of 21651905 is 50915612.

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

It is not a de Polignac number, because 21651905 - 2⁶ = 21651841 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21651907) 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, 196781 + ... + 196890.

It is an arithmetic number, because the mean of its divisors is an integer number (3543048).

Almost surely, 2^21651905 is an apocalyptic number.

It is an amenable number.

21651905 is a deficient number, since it is larger than the sum of its proper divisors (6692479).

21651905 is a wasteful number, since it uses less digits than its factorization.

21651905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 393687.

The product of its (nonzero) digits is 2700, while the sum is 29.

The square root of 21651905 is about 4653.1607537243. The cubic root of 21651905 is about 278.7182271896.

The spelling of 21651905 in words is "twenty-one million, six hundred fifty-one thousand, nine hundred five".