21351636 has 72 divisors (see below), whose sum is σ = 57081024. Its totient is φ = 6716160.

The previous prime is 21351619. The next prime is 21351637. The reversal of 21351636 is 63615312.

21351636 is a `hidden beast` number, since 21 + 3 + 5 + 1 + 636 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21351637) 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, 88476 + ... + 88716.

It is an arithmetic number, because the mean of its divisors is an integer number (792792).

Almost surely, 2^21351636 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 21351636, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28540512).

21351636 is an abundant number, since it is smaller than the sum of its proper divisors (35729388).

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

21351636 is a wasteful number, since it uses less digits than its factorization.

21351636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 381 (or 376 counting only the distinct ones).

The product of its digits is 3240, while the sum is 27.

The square root of 21351636 is about 4620.7830505229. The cubic root of 21351636 is about 277.4238018205.

Adding to 21351636 its reverse (63615312), we get a palindrome (84966948).

The spelling of 21351636 in words is "twenty-one million, three hundred fifty-one thousand, six hundred thirty-six".