21061643 has 4 divisors (see below), whose sum is σ = 21418680. Its totient is φ = 20704608.

The previous prime is 21061639. The next prime is 21061669. The reversal of 21061643 is 34616012.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21061643 - 2² = 21061639 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21061603) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 178430 + ... + 178547.

It is an arithmetic number, because the mean of its divisors is an integer number (5354670).

Almost surely, 2^21061643 is an apocalyptic number.

21061643 is a deficient number, since it is larger than the sum of its proper divisors (357037).

21061643 is an equidigital number, since it uses as much as digits as its factorization.

21061643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 357036.

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 21061643 is about 4589.2965691923. The cubic root of 21061643 is about 276.1621037154.

Adding to 21061643 its reverse (34616012), we get a palindrome (55677655).

The spelling of 21061643 in words is "twenty-one million, sixty-one thousand, six hundred forty-three".