21005975 has 6 divisors (see below), whose sum is σ = 26047440. Its totient is φ = 16804760.

The previous prime is 21005953. The next prime is 21005977. The reversal of 21005975 is 57950012.

It is not a de Polignac number, because 21005975 - 2¹² = 21001879 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21005977) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 420095 + ... + 420144.

It is an arithmetic number, because the mean of its divisors is an integer number (4341240).

Almost surely, 2^21005975 is an apocalyptic number.

21005975 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21005975 is a deficient number, since it is larger than the sum of its proper divisors (5041465).

21005975 is an equidigital number, since it uses as much as digits as its factorization.

21005975 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 840249 (or 840244 counting only the distinct ones).

The product of its (nonzero) digits is 3150, while the sum is 29.

The square root of 21005975 is about 4583.2275745374. The cubic root of 21005975 is about 275.9185811441.

Adding to 21005975 its reverse (57950012), we get a palindrome (78955987).

The spelling of 21005975 in words is "twenty-one million, five thousand, nine hundred seventy-five".