21300021 has 6 divisors (see below), whose sum is σ = 30766710. Its totient is φ = 14200008.

The previous prime is 21299987. The next prime is 21300029. The reversal of 21300021 is 12000312.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 21288996 + 11025 = 4614^2 + 105^2 .

It is not a de Polignac number, because 21300021 - 2¹¹ = 21297973 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9), and also a Moran number because the ratio is a prime number: 2366669 = 21300021 / (2 + 1 + 3 + 0 + 0 + 0 + 2 + 1).

It is a junction number, because it is equal to n+sod(n) for n = 21299976 and 21300012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21300029) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1183326 + ... + 1183343.

It is an arithmetic number, because the mean of its divisors is an integer number (5127785).

Almost surely, 2^21300021 is an apocalyptic number.

It is an amenable number.

21300021 is a deficient number, since it is larger than the sum of its proper divisors (9466689).

21300021 is a wasteful number, since it uses less digits than its factorization.

21300021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2366675 (or 2366672 counting only the distinct ones).

The product of its (nonzero) digits is 12, while the sum is 9.

The square root of 21300021 is about 4615.1945787800. The cubic root of 21300021 is about 277.2000752734.

Adding to 21300021 its reverse (12000312), we get a palindrome (33300333).

The spelling of 21300021 in words is "twenty-one million, three hundred thousand, twenty-one".