21041221 has 2 divisors, whose sum is σ = 21041222. Its totient is φ = 21041220.

The previous prime is 21041213. The next prime is 21041239. The reversal of 21041221 is 12214012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14861025 + 6180196 = 3855^2 + 2486^2 .

It is a cyclic number.

It is not a de Polignac number, because 21041221 - 2³ = 21041213 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21041201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10520610 + 10520611.

It is an arithmetic number, because the mean of its divisors is an integer number (10520611).

Almost surely, 2^21041221 is an apocalyptic number.

It is an amenable number.

21041221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21041221 is an equidigital number, since it uses as much as digits as its factorization.

21041221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21041221 is about 4587.0710698658. The cubic root of 21041221 is about 276.0728165011.

Adding to 21041221 its reverse (12214012), we get a palindrome (33255233).

The spelling of 21041221 in words is "twenty-one million, forty-one thousand, two hundred twenty-one".