21868551 has 12 divisors (see below), whose sum is σ = 31868928. Its totient is φ = 14449344.

The previous prime is 21868529. The next prime is 21868571. The reversal of 21868551 is 15586812.

21868551 is a `hidden beast` number, since 21 + 86 + 8 + 551 = 666.

It is not a de Polignac number, because 21868551 - 2⁵ = 21868519 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21868501) by changing a digit.

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 11 ways as a sum of consecutive naturals, for example, 9735 + ... + 11768.

It is an arithmetic number, because the mean of its divisors is an integer number (2655744).

Almost surely, 2^21868551 is an apocalyptic number.

21868551 is a deficient number, since it is larger than the sum of its proper divisors (10000377).

21868551 is a wasteful number, since it uses less digits than its factorization.

21868551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21622 (or 21619 counting only the distinct ones).

The product of its digits is 19200, while the sum is 36.

The square root of 21868551 is about 4676.3822555476. The cubic root of 21868551 is about 279.6447492953.

The spelling of 21868551 in words is "twenty-one million, eight hundred sixty-eight thousand, five hundred fifty-one".