21105665 has 16 divisors (see below), whose sum is σ = 29025408. Its totient is φ = 14432256.

The previous prime is 21105661. The next prime is 21105671. The reversal of 21105665 is 56650112.

It is a cyclic number.

It is not a de Polignac number, because 21105665 - 2² = 21105661 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21105661) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17729 + ... + 18881.

It is an arithmetic number, because the mean of its divisors is an integer number (1814088).

Almost surely, 2^21105665 is an apocalyptic number.

It is an amenable number.

21105665 is a deficient number, since it is larger than the sum of its proper divisors (7919743).

21105665 is a wasteful number, since it uses less digits than its factorization.

21105665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1688.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 21105665 is about 4594.0902254962. The cubic root of 21105665 is about 276.3543765883.

Adding to 21105665 its reverse (56650112), we get a palindrome (77755777).

The spelling of 21105665 in words is "twenty-one million, one hundred five thousand, six hundred sixty-five".