21758221 has 2 divisors, whose sum is σ = 21758222. Its totient is φ = 21758220.

The previous prime is 21758213. The next prime is 21758267. The reversal of 21758221 is 12285712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21288996 + 469225 = 4614^2 + 685^2 .

It is a cyclic number.

It is not a de Polignac number, because 21758221 - 2³ = 21758213 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21758221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21758291) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10879110 + 10879111.

It is an arithmetic number, because the mean of its divisors is an integer number (10879111).

Almost surely, 2^21758221 is an apocalyptic number.

It is an amenable number.

21758221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21758221 is an equidigital number, since it uses as much as digits as its factorization.

21758221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2240, while the sum is 28.

The square root of 21758221 is about 4664.5708269893. The cubic root of 21758221 is about 279.1736734659.

The spelling of 21758221 in words is "twenty-one million, seven hundred fifty-eight thousand, two hundred twenty-one".