21221515 has 16 divisors (see below), whose sum is σ = 30044160. Its totient is φ = 14081760.

The previous prime is 21221509. The next prime is 21221521. The reversal of 21221515 is 51512212.

It is an interprime number because it is at equal distance from previous prime (21221509) and next prime (21221521).

It is not a de Polignac number, because 21221515 - 2⁹ = 21221003 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21221492 and 21221501.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 8695 + ... + 10864.

It is an arithmetic number, because the mean of its divisors is an integer number (1877760).

Almost surely, 2^21221515 is an apocalyptic number.

21221515 is a deficient number, since it is larger than the sum of its proper divisors (8822645).

21221515 is a wasteful number, since it uses less digits than its factorization.

21221515 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19602.

The product of its digits is 200, while the sum is 19.

The square root of 21221515 is about 4606.6815605162. The cubic root of 21221515 is about 276.8590950138.

Adding to 21221515 its reverse (51512212), we get a palindrome (72733727).

It can be divided in two parts, 21221 and 515, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 21221515 in words is "twenty-one million, two hundred twenty-one thousand, five hundred fifteen".