21543965 has 4 divisors (see below), whose sum is σ = 25852764. Its totient is φ = 17235168.

The previous prime is 21543961. The next prime is 21544009. The reversal of 21543965 is 56934512.

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

It can be written as a sum of positive squares in 2 ways, for example, as 10106041 + 11437924 = 3179^2 + 3382^2 .

It is a cyclic number.

It is not a de Polignac number, because 21543965 - 2² = 21543961 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21543961) 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, 2154392 + ... + 2154401.

It is an arithmetic number, because the mean of its divisors is an integer number (6463191).

Almost surely, 2^21543965 is an apocalyptic number.

It is an amenable number.

21543965 is a deficient number, since it is larger than the sum of its proper divisors (4308799).

21543965 is an equidigital number, since it uses as much as digits as its factorization.

21543965 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4308798.

The product of its digits is 32400, while the sum is 35.

The square root of 21543965 is about 4641.5476944657. The cubic root of 21543965 is about 278.2542960669.

The spelling of 21543965 in words is "twenty-one million, five hundred forty-three thousand, nine hundred sixty-five".