21215124 has 72 divisors (see below), whose sum is σ = 63423360. Its totient is φ = 5850432.

The previous prime is 21215111. The next prime is 21215137. The reversal of 21215124 is 42151212.

It is an interprime number because it is at equal distance from previous prime (21215111) and next prime (21215137).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a junction number, because it is equal to n+sod(n) for n = 21215097 and 21215106.

It is a congruent number.

It is an unprimeable number.

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 23 ways as a sum of consecutive naturals, for example, 5857 + ... + 8759.

It is an arithmetic number, because the mean of its divisors is an integer number (880880).

Almost surely, 2^21215124 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21215124, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31711680).

21215124 is an abundant number, since it is smaller than the sum of its proper divisors (42208236).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21215124 is a wasteful number, since it uses less digits than its factorization.

21215124 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2949 (or 2944 counting only the distinct ones).

The product of its digits is 160, while the sum is 18.

The square root of 21215124 is about 4605.9878419292. The cubic root of 21215124 is about 276.8312995724.

Adding to 21215124 its reverse (42151212), we get a palindrome (63366336).

The spelling of 21215124 in words is "twenty-one million, two hundred fifteen thousand, one hundred twenty-four".