21381615 has 12 divisors (see below), whose sum is σ = 37061544. Its totient is φ = 11403504.

The previous prime is 21381611. The next prime is 21381617. The reversal of 21381615 is 51618312.

It is not a de Polignac number, because 21381615 - 2² = 21381611 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21381611) 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, 237529 + ... + 237618.

It is an arithmetic number, because the mean of its divisors is an integer number (3088462).

Almost surely, 2^21381615 is an apocalyptic number.

21381615 is a deficient number, since it is larger than the sum of its proper divisors (15679929).

21381615 is a wasteful number, since it uses less digits than its factorization.

21381615 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 475158 (or 475155 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 21381615 is about 4624.0258433534. The cubic root of 21381615 is about 277.5535810829.

Adding to 21381615 its reverse (51618312), we get a palindrome (72999927).

The spelling of 21381615 in words is "twenty-one million, three hundred eighty-one thousand, six hundred fifteen".