21640065 has 32 divisors (see below), whose sum is σ = 37034496. Its totient is φ = 10752000.

The previous prime is 21640063. The next prime is 21640067. The reversal of 21640065 is 56004612.

It is an interprime number because it is at equal distance from previous prime (21640063) and next prime (21640067).

It is not a de Polignac number, because 21640065 - 2¹ = 21640063 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21640063) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 28440 + ... + 29190.

It is an arithmetic number, because the mean of its divisors is an integer number (1157328).

Almost surely, 2^21640065 is an apocalyptic number.

It is an amenable number.

21640065 is a deficient number, since it is larger than the sum of its proper divisors (15394431).

21640065 is a wasteful number, since it uses less digits than its factorization.

21640065 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 889.

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21640065 is about 4651.8883262606. Note that the first 3 decimals coincide. The cubic root of 21640065 is about 278.6674137159.

Adding to 21640065 its reverse (56004612), we get a palindrome (77644677).

The spelling of 21640065 in words is "twenty-one million, six hundred forty thousand, sixty-five".