21051636 has 12 divisors (see below), whose sum is σ = 49120512. Its totient is φ = 7017208.

The previous prime is 21051623. The next prime is 21051637. The reversal of 21051636 is 63615012.

It is a tau number, because it is divible by the number of its divisors (12).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21051637) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 877140 + ... + 877163.

It is an arithmetic number, because the mean of its divisors is an integer number (4093376).

Almost surely, 2^21051636 is an apocalyptic number.

It is an amenable number.

21051636 is an abundant number, since it is smaller than the sum of its proper divisors (28068876).

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

21051636 is a wasteful number, since it uses less digits than its factorization.

21051636 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1754310 (or 1754308 counting only the distinct ones).

The product of its (nonzero) digits is 1080, while the sum is 24.

The square root of 21051636 is about 4588.2061854280. The cubic root of 21051636 is about 276.1183592337.

Adding to 21051636 its reverse (63615012), we get a palindrome (84666648).

It can be divided in two parts, 2105 and 1636, that added together give a triangular number (3741 = T₈₆).

The spelling of 21051636 in words is "twenty-one million, fifty-one thousand, six hundred thirty-six".