21168821 has 2 divisors, whose sum is σ = 21168822. Its totient is φ = 21168820.

The previous prime is 21168817. The next prime is 21168827. The reversal of 21168821 is 12886112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19704721 + 1464100 = 4439^2 + 1210^2 .

It is a cyclic number.

It is not a de Polignac number, because 21168821 - 2² = 21168817 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21168827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10584410 + 10584411.

It is an arithmetic number, because the mean of its divisors is an integer number (10584411).

Almost surely, 2^21168821 is an apocalyptic number.

It is an amenable number.

21168821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21168821 is an equidigital number, since it uses as much as digits as its factorization.

21168821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1536, while the sum is 29.

The square root of 21168821 is about 4600.9587044441. The cubic root of 21168821 is about 276.6297537889.

The spelling of 21168821 in words is "twenty-one million, one hundred sixty-eight thousand, eight hundred twenty-one".