21861015 has 16 divisors (see below), whose sum is σ = 38157696. Its totient is φ = 10599200.

The previous prime is 21861013. The next prime is 21861019. The reversal of 21861015 is 51016812.

It is not a de Polignac number, because 21861015 - 2¹ = 21861013 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21861013) 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 15 ways as a sum of consecutive naturals, for example, 66081 + ... + 66410.

It is an arithmetic number, because the mean of its divisors is an integer number (2384856).

Almost surely, 2^21861015 is an apocalyptic number.

21861015 is a deficient number, since it is larger than the sum of its proper divisors (16296681).

21861015 is a wasteful number, since it uses less digits than its factorization.

21861015 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 132510.

The product of its (nonzero) digits is 480, while the sum is 24.

The square root of 21861015 is about 4675.5764350505. The cubic root of 21861015 is about 279.6126233297.

Adding to 21861015 its reverse (51016812), we get a palindrome (72877827).

The spelling of 21861015 in words is "twenty-one million, eight hundred sixty-one thousand, fifteen".