21243437 has 2 divisors, whose sum is σ = 21243438. Its totient is φ = 21243436.

The previous prime is 21243403. The next prime is 21243473. The reversal of 21243437 is 73434212.

Together with next prime (21243473) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12752041 + 8491396 = 3571^2 + 2914^2 .

It is a cyclic number.

It is not a de Polignac number, because 21243437 - 2⁸ = 21243181 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21243137) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10621718 + 10621719.

It is an arithmetic number, because the mean of its divisors is an integer number (10621719).

Almost surely, 2^21243437 is an apocalyptic number.

It is an amenable number.

21243437 is a deficient number, since it is larger than the sum of its proper divisors (1).

21243437 is an equidigital number, since it uses as much as digits as its factorization.

21243437 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4032, while the sum is 26.

The square root of 21243437 is about 4609.0603163769. The cubic root of 21243437 is about 276.9543947823.

Adding to 21243437 its reverse (73434212), we get a palindrome (94677649).

The spelling of 21243437 in words is "twenty-one million, two hundred forty-three thousand, four hundred thirty-seven".