21215656 has 96 divisors (see below), whose sum is σ = 52093440. Its totient is φ = 7920000.

The previous prime is 21215627. The next prime is 21215657. The reversal of 21215656 is 65651212.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (21215657) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 210006 + ... + 210106.

It is an arithmetic number, because the mean of its divisors is an integer number (542640).

Almost surely, 2^21215656 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 21215656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26046720).

21215656 is an abundant number, since it is smaller than the sum of its proper divisors (30877784).

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

21215656 is a wasteful number, since it uses less digits than its factorization.

21215656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 167 (or 152 counting only the distinct ones).

The product of its digits is 3600, while the sum is 28.

The square root of 21215656 is about 4606.0455924795. The cubic root of 21215656 is about 276.8336135352.

Adding to 21215656 its reverse (65651212), we get a palindrome (86866868).

Subtracting 21215656 from its reverse (65651212), we obtain a square (44435556 = 6666²).

It can be divided in two parts, 212156 and 56, that added together give a palindrome (212212).

The spelling of 21215656 in words is "twenty-one million, two hundred fifteen thousand, six hundred fifty-six".