21720168 has 24 divisors (see below), whose sum is σ = 58825650. Its totient is φ = 7240032.

The previous prime is 21720137. The next prime is 21720197. The reversal of 21720168 is 86102712.

It can be written as a sum of positive squares in only one way, i.e., 19342404 + 2377764 = 4398^2 + 1542^2 .

It is a tau number, because it is divible by the number of its divisors (24).

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 150763 + ... + 150906.

Almost surely, 2^21720168 is an apocalyptic number.

It is an amenable number.

21720168 is an abundant number, since it is smaller than the sum of its proper divisors (37105482).

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

21720168 is a wasteful number, since it uses less digits than its factorization.

21720168 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 301681 (or 301674 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21720168 is about 4660.4901029827. The cubic root of 21720168 is about 279.0108293480.

The spelling of 21720168 in words is "twenty-one million, seven hundred twenty thousand, one hundred sixty-eight".