21642786 has 72 divisors (see below), whose sum is σ = 54359760. Its totient is φ = 6201360.

The previous prime is 21642773. The next prime is 21642791. The reversal of 21642786 is 68724612.

21642786 is a `hidden beast` number, since 2 + 1 + 642 + 7 + 8 + 6 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 21642786.

It is an unprimeable number.

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 35 ways as a sum of consecutive naturals, for example, 41121 + ... + 41643.

Almost surely, 2^21642786 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21642786, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27179880).

21642786 is an abundant number, since it is smaller than the sum of its proper divisors (32716974).

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

21642786 is a wasteful number, since it uses less digits than its factorization.

21642786 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 572 (or 558 counting only the distinct ones).

The product of its digits is 32256, while the sum is 36.

The square root of 21642786 is about 4652.1807789466. The cubic root of 21642786 is about 278.6790930131.

It can be divided in two parts, 2164 and 2786, that added together give a triangular number (4950 = T₉₉).

The spelling of 21642786 in words is "twenty-one million, six hundred forty-two thousand, seven hundred eighty-six".