21240643 has 2 divisors, whose sum is σ = 21240644. Its totient is φ = 21240642.

The previous prime is 21240631. The next prime is 21240683. The reversal of 21240643 is 34604212.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21240643 - 2¹³ = 21232451 is a prime.

It is equal to p_1344163 and since 21240643 and 1344163 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21240683) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10620321 + 10620322.

It is an arithmetic number, because the mean of its divisors is an integer number (10620322).

Almost surely, 2^21240643 is an apocalyptic number.

21240643 is a deficient number, since it is larger than the sum of its proper divisors (1).

21240643 is an equidigital number, since it uses as much as digits as its factorization.

21240643 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1152, while the sum is 22.

The square root of 21240643 is about 4608.7572077513. The cubic root of 21240643 is about 276.9422522948.

Adding to 21240643 its reverse (34604212), we get a palindrome (55844855).

The spelling of 21240643 in words is "twenty-one million, two hundred forty thousand, six hundred forty-three".