21213556 has 36 divisors (see below), whose sum is σ = 45952032. Its totient is φ = 8390304.

The previous prime is 21213553. The next prime is 21213559. The reversal of 21213556 is 65531212.

It is an interprime number because it is at equal distance from previous prime (21213553) and next prime (21213559).

It is a self number, because there is not a number n which added to its sum of digits gives 21213556.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21213553) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2491 + ... + 6973.

Almost surely, 2^21213556 is an apocalyptic number.

21213556 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21213556, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22976016).

21213556 is an abundant number, since it is smaller than the sum of its proper divisors (24738476).

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

21213556 is a wasteful number, since it uses less digits than its factorization.

21213556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4520 (or 4505 counting only the distinct ones).

The product of its digits is 1800, while the sum is 25.

The square root of 21213556 is about 4605.8176255688. The cubic root of 21213556 is about 276.8244792466.

Adding to 21213556 its reverse (65531212), we get a palindrome (86744768).

The spelling of 21213556 in words is "twenty-one million, two hundred thirteen thousand, five hundred fifty-six".