21615887 has 4 divisors (see below), whose sum is σ = 21631440. Its totient is φ = 21600336.

The previous prime is 21615871. The next prime is 21615907. The reversal of 21615887 is 78851612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21615887 - 2⁴ = 21615871 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21615887.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21615287) 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 3 ways as a sum of consecutive naturals, for example, 5462 + ... + 8547.

It is an arithmetic number, because the mean of its divisors is an integer number (5407860).

Almost surely, 2^21615887 is an apocalyptic number.

21615887 is a deficient number, since it is larger than the sum of its proper divisors (15553).

21615887 is a wasteful number, since it uses less digits than its factorization.

21615887 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15552.

The product of its digits is 26880, while the sum is 38.

The square root of 21615887 is about 4649.2888703543. The cubic root of 21615887 is about 278.5635919150.

The spelling of 21615887 in words is "twenty-one million, six hundred fifteen thousand, eight hundred eighty-seven".