21663568 has 10 divisors (see below), whose sum is σ = 41973194. Its totient is φ = 10831776.

The previous prime is 21663547. The next prime is 21663589. The reversal of 21663568 is 86536612.

It is an interprime number because it is at equal distance from previous prime (21663547) and next prime (21663589).

It can be written as a sum of positive squares in only one way, i.e., 20903184 + 760384 = 4572^2 + 872^2 .

It is a congruent number.

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 as a sum of consecutive naturals, namely, 676971 + ... + 677002.

Almost surely, 2^21663568 is an apocalyptic number.

It is an amenable number.

21663568 is a deficient number, since it is larger than the sum of its proper divisors (20309626).

21663568 is a wasteful number, since it uses less digits than its factorization.

21663568 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1353981 (or 1353975 counting only the distinct ones).

The product of its digits is 51840, while the sum is 37.

The square root of 21663568 is about 4654.4138191613. The cubic root of 21663568 is about 278.7682629283.

The spelling of 21663568 in words is "twenty-one million, six hundred sixty-three thousand, five hundred sixty-eight".