21212505 has 12 divisors (see below), whose sum is σ = 36768420. Its totient is φ = 11313312.

The previous prime is 21212501. The next prime is 21212519. The reversal of 21212505 is 50521212.

It can be written as a sum of positive squares in 2 ways, for example, as 15116544 + 6095961 = 3888^2 + 2469^2 .

It is not a de Polignac number, because 21212505 - 2² = 21212501 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (21212501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 235650 + ... + 235739.

It is an arithmetic number, because the mean of its divisors is an integer number (3064035).

Almost surely, 2^21212505 is an apocalyptic number.

It is an amenable number.

21212505 is a deficient number, since it is larger than the sum of its proper divisors (15555915).

21212505 is a wasteful number, since it uses less digits than its factorization.

21212505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 471400 (or 471397 counting only the distinct ones).

The product of its (nonzero) digits is 200, while the sum is 18.

The square root of 21212505 is about 4605.7035293210. The cubic root of 21212505 is about 276.8199075264.

Adding to 21212505 its reverse (50521212), we get a palindrome (71733717).

The spelling of 21212505 in words is "twenty-one million, two hundred twelve thousand, five hundred five".