21681065 has 24 divisors (see below), whose sum is σ = 31109568. Its totient is φ = 14208480.

The previous prime is 21681061. The next prime is 21681091. The reversal of 21681065 is 56018612.

21681065 = T₁₉₄ + T₁₉₅ + ... + T₅₁₅.

It is a happy number.

It is not a de Polignac number, because 21681065 - 2² = 21681061 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21681061) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 17930 + ... + 19100.

It is an arithmetic number, because the mean of its divisors is an integer number (1296232).

Almost surely, 2^21681065 is an apocalyptic number.

It is an amenable number.

21681065 is a deficient number, since it is larger than the sum of its proper divisors (9428503).

21681065 is a wasteful number, since it uses less digits than its factorization.

21681065 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1229 (or 1206 counting only the distinct ones).

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 21681065 is about 4656.2930534922. The cubic root of 21681065 is about 278.8432935930.

Adding to 21681065 its reverse (56018612), we get a palindrome (77699677).

The spelling of 21681065 in words is "twenty-one million, six hundred eighty-one thousand, sixty-five".