21709905 has 32 divisors (see below), whose sum is σ = 39936000. Its totient is φ = 9865152.

The previous prime is 21709903. The next prime is 21709921. The reversal of 21709905 is 50990712.

It is not a de Polignac number, because 21709905 - 2¹ = 21709903 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21709903) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 20376 + ... + 21414.

It is an arithmetic number, because the mean of its divisors is an integer number (1248000).

Almost surely, 2^21709905 is an apocalyptic number.

It is an amenable number.

21709905 is a deficient number, since it is larger than the sum of its proper divisors (18226095).

21709905 is a wasteful number, since it uses less digits than its factorization.

21709905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1253.

The product of its (nonzero) digits is 5670, while the sum is 33.

The square root of 21709905 is about 4659.3889084299. The cubic root of 21709905 is about 278.9668772744.

The spelling of 21709905 in words is "twenty-one million, seven hundred nine thousand, nine hundred five".