21356643 has 32 divisors (see below), whose sum is σ = 36126720. Its totient is φ = 10899360.

The previous prime is 21356633. The next prime is 21356653. The reversal of 21356643 is 34665312.

It is an interprime number because it is at equal distance from previous prime (21356633) and next prime (21356653).

It is not a de Polignac number, because 21356643 - 2⁵ = 21356611 is a prime.

It is a super-2 number, since 2×21356643² = 912212400458898, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21356643.

It is not an unprimeable number, because it can be changed into a prime (21356603) 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 31 ways as a sum of consecutive naturals, for example, 12846 + ... + 14412.

It is an arithmetic number, because the mean of its divisors is an integer number (1128960).

Almost surely, 2^21356643 is an apocalyptic number.

21356643 is a deficient number, since it is larger than the sum of its proper divisors (14770077).

21356643 is a wasteful number, since it uses less digits than its factorization.

21356643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1647.

The product of its digits is 12960, while the sum is 30.

The square root of 21356643 is about 4621.3248100518. The cubic root of 21356643 is about 277.4454855986.

It can be divided in two parts, 2135 and 6643, that added together give a palindrome (8778).

The spelling of 21356643 in words is "twenty-one million, three hundred fifty-six thousand, six hundred forty-three".