21323261 has 2 divisors, whose sum is σ = 21323262. Its totient is φ = 21323260.

The previous prime is 21323209. The next prime is 21323273. The reversal of 21323261 is 16232312.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17347225 + 3976036 = 4165^2 + 1994^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21323261 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21323161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10661630 + 10661631.

It is an arithmetic number, because the mean of its divisors is an integer number (10661631).

Almost surely, 2^21323261 is an apocalyptic number.

It is an amenable number.

21323261 is a deficient number, since it is larger than the sum of its proper divisors (1).

21323261 is an equidigital number, since it uses as much as digits as its factorization.

21323261 is an evil number, because the sum of its binary digits is even.

The product of its digits is 432, while the sum is 20.

The square root of 21323261 is about 4617.7116627178. The cubic root of 21323261 is about 277.3008543323.

Adding to 21323261 its reverse (16232312), we get a palindrome (37555573).

The spelling of 21323261 in words is "twenty-one million, three hundred twenty-three thousand, two hundred sixty-one".