21121205 has 12 divisors (see below), whose sum is σ = 29483820. Its totient is φ = 14482944.

The previous prime is 21121201. The next prime is 21121207. The reversal of 21121205 is 50212112.

It can be written as a sum of positive squares in 2 ways, for example, as 3598609 + 17522596 = 1897^2 + 4186^2 .

It is not a de Polignac number, because 21121205 - 2² = 21121201 is a prime.

It is a super-2 number, since 2×21121205² = 892210601304050, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21121205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121201) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 42860 + ... + 43349.

It is an arithmetic number, because the mean of its divisors is an integer number (2456985).

Almost surely, 2^21121205 is an apocalyptic number.

It is an amenable number.

21121205 is a deficient number, since it is larger than the sum of its proper divisors (8362615).

21121205 is an equidigital number, since it uses as much as digits as its factorization.

21121205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86228 (or 86221 counting only the distinct ones).

The product of its (nonzero) digits is 40, while the sum is 14.

The square root of 21121205 is about 4595.7812175951. The cubic root of 21121205 is about 276.4221860828.

Adding to 21121205 its reverse (50212112), we get a palindrome (71333317).

The spelling of 21121205 in words is "twenty-one million, one hundred twenty-one thousand, two hundred five".