21865121 has 2 divisors, whose sum is σ = 21865122. Its totient is φ = 21865120.

The previous prime is 21865099. The next prime is 21865133. The reversal of 21865121 is 12156812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21752896 + 112225 = 4664^2 + 335^2 .

It is a cyclic number.

It is not a de Polignac number, because 21865121 - 2⁶ = 21865057 is a prime.

It is not a weakly prime, because it can be changed into another prime (21865141) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10932560 + 10932561.

It is an arithmetic number, because the mean of its divisors is an integer number (10932561).

Almost surely, 2^21865121 is an apocalyptic number.

It is an amenable number.

21865121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21865121 is an equidigital number, since it uses as much as digits as its factorization.

21865121 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 960, while the sum is 26.

The square root of 21865121 is about 4676.0155046792. The cubic root of 21865121 is about 279.6301281217.

The spelling of 21865121 in words is "twenty-one million, eight hundred sixty-five thousand, one hundred twenty-one".