21651968 has 40 divisors (see below), whose sum is σ = 46603788. Its totient is φ = 9990144.

The previous prime is 21651967. The next prime is 21651979. The reversal of 21651968 is 86915612.

It can be written as a sum of positive squares in 2 ways, for example, as 21086464 + 565504 = 4592^2 + 752^2 .

It is not an unprimeable number, because it can be changed into a prime (21651967) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5030 + ... + 8282.

Almost surely, 2^21651968 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21651968, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23301894).

21651968 is an abundant number, since it is smaller than the sum of its proper divisors (24951820).

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

21651968 is an equidigital number, since it uses as much as digits as its factorization.

21651968 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3284 (or 3268 counting only the distinct ones).

The product of its digits is 25920, while the sum is 38.

The square root of 21651968 is about 4653.1675233114. The cubic root of 21651968 is about 278.7184975158.

The spelling of 21651968 in words is "twenty-one million, six hundred fifty-one thousand, nine hundred sixty-eight".