21385551 has 8 divisors (see below), whose sum is σ = 31106304. Its totient is φ = 12960920.

The previous prime is 21385549. The next prime is 21385591. The reversal of 21385551 is 15558312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21385551 - 2¹ = 21385549 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21385591) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 323991 + ... + 324056.

It is an arithmetic number, because the mean of its divisors is an integer number (3888288).

Almost surely, 2^21385551 is an apocalyptic number.

21385551 is a deficient number, since it is larger than the sum of its proper divisors (9720753).

21385551 is a wasteful number, since it uses less digits than its factorization.

21385551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 648061.

The product of its digits is 6000, while the sum is 30.

The square root of 21385551 is about 4624.4514269262. The cubic root of 21385551 is about 277.5706110386.

The spelling of 21385551 in words is "twenty-one million, three hundred eighty-five thousand, five hundred fifty-one".