21005907 has 16 divisors (see below), whose sum is σ = 30616320. Its totient is φ = 12732192.

The previous prime is 21005903. The next prime is 21005953. The reversal of 21005907 is 70950012.

It is not a de Polignac number, because 21005907 - 2² = 21005903 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21005903) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1407 + ... + 6632.

It is an arithmetic number, because the mean of its divisors is an integer number (1913520).

Almost surely, 2^21005907 is an apocalyptic number.

21005907 is a deficient number, since it is larger than the sum of its proper divisors (9610413).

21005907 is a wasteful number, since it uses less digits than its factorization.

21005907 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8122.

The product of its (nonzero) digits is 630, while the sum is 24.

The square root of 21005907 is about 4583.2201561784. The cubic root of 21005907 is about 275.9182834116.

Adding to 21005907 its reverse (70950012), we get a palindrome (91955919).

It can be divided in two parts, 21005 and 907, that added together give a palindrome (21912).

The spelling of 21005907 in words is "twenty-one million, five thousand, nine hundred seven".