21215543 has 2 divisors, whose sum is σ = 21215544. Its totient is φ = 21215542.

The previous prime is 21215539. The next prime is 21215561. The reversal of 21215543 is 34551212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21215543 - 2² = 21215539 is a prime.

It is a super-4 number, since 4×21215543⁴ (a number of 30 digits) contains 4444 as substring.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21215503) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10607771 + 10607772.

It is an arithmetic number, because the mean of its divisors is an integer number (10607772).

Almost surely, 2^21215543 is an apocalyptic number.

21215543 is a deficient number, since it is larger than the sum of its proper divisors (1).

21215543 is an equidigital number, since it uses as much as digits as its factorization.

21215543 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1200, while the sum is 23.

The square root of 21215543 is about 4606.0333259758. The cubic root of 21215543 is about 276.8331220388.

Adding to 21215543 its reverse (34551212), we get a palindrome (55766755).

The spelling of 21215543 in words is "twenty-one million, two hundred fifteen thousand, five hundred forty-three".