21642551 has 8 divisors (see below), whose sum is σ = 24954144. Its totient is φ = 18385920.

The previous prime is 21642527. The next prime is 21642553. The reversal of 21642551 is 15524612.

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

It is not a de Polignac number, because 21642551 - 2⁶ = 21642487 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21642551.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21642553) 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, 12890 + ... + 14471.

It is an arithmetic number, because the mean of its divisors is an integer number (3119268).

Almost surely, 2^21642551 is an apocalyptic number.

21642551 is a deficient number, since it is larger than the sum of its proper divisors (3311593).

21642551 is a wasteful number, since it uses less digits than its factorization.

21642551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27481.

The product of its digits is 2400, while the sum is 26.

The square root of 21642551 is about 4652.1555219059. The cubic root of 21642551 is about 278.6780843657.

The spelling of 21642551 in words is "twenty-one million, six hundred forty-two thousand, five hundred fifty-one".