21368551 has 4 divisors (see below), whose sum is σ = 21399400. Its totient is φ = 21337704.

The previous prime is 21368539. The next prime is 21368569. The reversal of 21368551 is 15586312.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21368551 - 2¹¹ = 21366503 is a prime.

It is a super-3 number, since 3×21368551³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21368531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 14361 + ... + 15778.

It is an arithmetic number, because the mean of its divisors is an integer number (5349850).

Almost surely, 2^21368551 is an apocalyptic number.

21368551 is a deficient number, since it is larger than the sum of its proper divisors (30849).

21368551 is an equidigital number, since it uses as much as digits as its factorization.

21368551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30848.

The product of its digits is 7200, while the sum is 31.

The square root of 21368551 is about 4622.6130056495. The cubic root of 21368551 is about 277.4970418752.

The spelling of 21368551 in words is "twenty-one million, three hundred sixty-eight thousand, five hundred fifty-one".