21520001 has 4 divisors (see below), whose sum is σ = 22262100. Its totient is φ = 20777904.

The previous prime is 21519929. The next prime is 21520003. The reversal of 21520001 is 10002512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 4906225 + 16613776 = 2215^2 + 4076^2 .

It is a cyclic number.

It is not a de Polignac number, because 21520001 - 2¹⁴ = 21503617 is a prime.

It is a super-2 number, since 2×21520001² = 926220886080002, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21520003) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 371006 + ... + 371063.

It is an arithmetic number, because the mean of its divisors is an integer number (5565525).

Almost surely, 2^21520001 is an apocalyptic number.

It is an amenable number.

21520001 is a deficient number, since it is larger than the sum of its proper divisors (742099).

21520001 is an equidigital number, since it uses as much as digits as its factorization.

21520001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 742098.

The product of its (nonzero) digits is 20, while the sum is 11.

The square root of 21520001 is about 4638.9655096799. The cubic root of 21520001 is about 278.1510875837.

Adding to 21520001 its reverse (10002512), we get a palindrome (31522513).

The spelling of 21520001 in words is "twenty-one million, five hundred twenty thousand, one".