21645001 has 16 divisors (see below), whose sum is σ = 25968384. Its totient is φ = 17639424.

The previous prime is 21644969. The next prime is 21645023. The reversal of 21645001 is 10054612.

It is a cyclic number.

It is not a de Polignac number, because 21645001 - 2⁵ = 21644969 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21645001.

It is not an unprimeable number, because it can be changed into a prime (21645101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37225 + ... + 37801.

It is an arithmetic number, because the mean of its divisors is an integer number (1623024).

Almost surely, 2^21645001 is an apocalyptic number.

It is an amenable number.

21645001 is a deficient number, since it is larger than the sum of its proper divisors (4323383).

21645001 is a wasteful number, since it uses less digits than its factorization.

21645001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 840.

The product of its (nonzero) digits is 240, while the sum is 19.

The square root of 21645001 is about 4652.4188332522. The cubic root of 21645001 is about 278.6885996933.

Adding to 21645001 its reverse (10054612), we get a palindrome (31699613).

The spelling of 21645001 in words is "twenty-one million, six hundred forty-five thousand, one".