21009615 has 16 divisors (see below), whose sum is σ = 36671616. Its totient is φ = 10186400.

The previous prime is 21009613. The next prime is 21009617. The reversal of 21009615 is 51690012.

It is an interprime number because it is at equal distance from previous prime (21009613) and next prime (21009617).

It is not a de Polignac number, because 21009615 - 2¹ = 21009613 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21009613) by changing a digit.

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, 63501 + ... + 63830.

It is an arithmetic number, because the mean of its divisors is an integer number (2291976).

Almost surely, 2^21009615 is an apocalyptic number.

21009615 is a deficient number, since it is larger than the sum of its proper divisors (15662001).

21009615 is a wasteful number, since it uses less digits than its factorization.

21009615 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 127350.

The product of its (nonzero) digits is 540, while the sum is 24.

The square root of 21009615 is about 4583.6246574082. The cubic root of 21009615 is about 275.9345176515.

Adding to 21009615 its reverse (51690012), we get a palindrome (72699627).

The spelling of 21009615 in words is "twenty-one million, nine thousand, six hundred fifteen".