21820551 has 8 divisors (see below), whose sum is σ = 29145984. Its totient is φ = 14521080.

The previous prime is 21820543. The next prime is 21820553. The reversal of 21820551 is 15502812.

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

It is not a de Polignac number, because 21820551 - 2³ = 21820543 is a prime.

It is a super-2 number, since 2×21820551² = 952272891887202, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21820553) 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 7 ways as a sum of consecutive naturals, for example, 4435 + ... + 7956.

It is an arithmetic number, because the mean of its divisors is an integer number (3643248).

Almost surely, 2^21820551 is an apocalyptic number.

21820551 is a deficient number, since it is larger than the sum of its proper divisors (7325433).

21820551 is a wasteful number, since it uses less digits than its factorization.

21820551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12981.

The product of its (nonzero) digits is 800, while the sum is 24.

The square root of 21820551 is about 4671.2472638472. The cubic root of 21820551 is about 279.4399989397.

The spelling of 21820551 in words is "twenty-one million, eight hundred twenty thousand, five hundred fifty-one".