21571668 has 18 divisors (see below), whose sum is σ = 54528474. Its totient is φ = 7190544.

The previous prime is 21571651. The next prime is 21571673. The reversal of 21571668 is 86617512.

21571668 is a `hidden beast` number, since 21 + 571 + 6 + 68 = 666.

It can be written as a sum of positive squares in only one way, i.e., 20684304 + 887364 = 4548^2 + 942^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 599213 = 21571668 / (2 + 1 + 5 + 7 + 1 + 6 + 6 + 8).

It is a congruent number.

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, 299571 + ... + 299642.

Almost surely, 2^21571668 is an apocalyptic number.

It is an amenable number.

21571668 is an abundant number, since it is smaller than the sum of its proper divisors (32956806).

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

21571668 is a wasteful number, since it uses less digits than its factorization.

21571668 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 599223 (or 599218 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21571668 is about 4644.5309773970. The cubic root of 21571668 is about 278.3735123928.

The spelling of 21571668 in words is "twenty-one million, five hundred seventy-one thousand, six hundred sixty-eight".