21213656 has 8 divisors (see below), whose sum is σ = 39775620. Its totient is φ = 10606824.

The previous prime is 21213631. The next prime is 21213667. The reversal of 21213656 is 65631212.

It is a tau number, because it is divible by the number of its divisors (8).

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, 1325846 + ... + 1325861.

Almost surely, 2^21213656 is an apocalyptic number.

It is an amenable number.

21213656 is a deficient number, since it is larger than the sum of its proper divisors (18561964).

21213656 is a wasteful number, since it uses less digits than its factorization.

21213656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2651713 (or 2651709 counting only the distinct ones).

The product of its digits is 2160, while the sum is 26.

The square root of 21213656 is about 4605.8284813918. The cubic root of 21213656 is about 276.8249142264.

Adding to 21213656 its reverse (65631212), we get a palindrome (86844868).

The spelling of 21213656 in words is "twenty-one million, two hundred thirteen thousand, six hundred fifty-six".