21236921 has 2 divisors, whose sum is σ = 21236922. Its totient is φ = 21236920.

The previous prime is 21236909. The next prime is 21236947. The reversal of 21236921 is 12963212.

It is an a-pointer prime, because the next prime (21236947) can be obtained adding 21236921 to its sum of digits (26).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13424896 + 7812025 = 3664^2 + 2795^2 .

It is a cyclic number.

It is not a de Polignac number, because 21236921 - 2⁶ = 21236857 is a prime.

It is a Sophie Germain prime.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21236951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10618460 + 10618461.

It is an arithmetic number, because the mean of its divisors is an integer number (10618461).

Almost surely, 2^21236921 is an apocalyptic number.

It is an amenable number.

21236921 is a deficient number, since it is larger than the sum of its proper divisors (1).

21236921 is an equidigital number, since it uses as much as digits as its factorization.

21236921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1296, while the sum is 26.

The square root of 21236921 is about 4608.3533935669. The cubic root of 21236921 is about 276.9260751436.

The spelling of 21236921 in words is "twenty-one million, two hundred thirty-six thousand, nine hundred twenty-one".