21505001 has 8 divisors (see below), whose sum is σ = 24980544. Its totient is φ = 18130320.

The previous prime is 21504971. The next prime is 21505007. The reversal of 21505001 is 10050512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21505001 - 2¹⁸ = 21242857 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21505007) 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 7 ways as a sum of consecutive naturals, for example, 24755 + ... + 25608.

It is an arithmetic number, because the mean of its divisors is an integer number (3122568).

Almost surely, 2^21505001 is an apocalyptic number.

It is an amenable number.

21505001 is a deficient number, since it is larger than the sum of its proper divisors (3475543).

21505001 is an equidigital number, since it uses as much as digits as its factorization.

21505001 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50431.

The product of its (nonzero) digits is 50, while the sum is 14.

The square root of 21505001 is about 4637.3484880910. The cubic root of 21505001 is about 278.0864463834.

Adding to 21505001 its reverse (10050512), we get a palindrome (31555513).

The spelling of 21505001 in words is "twenty-one million, five hundred five thousand, one".