21236021 has 2 divisors, whose sum is σ = 21236022. Its totient is φ = 21236020.

The previous prime is 21235999. The next prime is 21236041. The reversal of 21236021 is 12063212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17757796 + 3478225 = 4214^2 + 1865^2 .

It is a cyclic number.

It is not a de Polignac number, because 21236021 - 2¹⁸ = 20973877 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21236041) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10618010 + 10618011.

It is an arithmetic number, because the mean of its divisors is an integer number (10618011).

Almost surely, 2^21236021 is an apocalyptic number.

It is an amenable number.

21236021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21236021 is an equidigital number, since it uses as much as digits as its factorization.

21236021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 144, while the sum is 17.

The square root of 21236021 is about 4608.2557437712. The cubic root of 21236021 is about 276.9221631360.

Adding to 21236021 its reverse (12063212), we get a palindrome (33299233).

The spelling of 21236021 in words is "twenty-one million, two hundred thirty-six thousand, twenty-one".