21043636 has 6 divisors (see below), whose sum is σ = 36826370. Its totient is φ = 10521816.

The previous prime is 21043613. The next prime is 21043661. The reversal of 21043636 is 63634012.

It can be written as a sum of positive squares in only one way, i.e., 20304036 + 739600 = 4506^2 + 860^2 .

It is a super-2 number, since 2×21043636² = 885669232200992, which contains 22 as substring.

21043636 is a modest number, since divided by 3636 gives 2104 as remainder.

It is a self number, because there is not a number n which added to its sum of digits gives 21043636.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2630451 + ... + 2630458.

Almost surely, 2^21043636 is an apocalyptic number.

It is an amenable number.

21043636 is a deficient number, since it is larger than the sum of its proper divisors (15782734).

21043636 is a wasteful number, since it uses less digits than its factorization.

21043636 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5260913 (or 5260911 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 25.

The square root of 21043636 is about 4587.3343021847. The cubic root of 21043636 is about 276.0833781560.

Adding to 21043636 its reverse (63634012), we get a palindrome (84677648).

The spelling of 21043636 in words is "twenty-one million, forty-three thousand, six hundred thirty-six".