21421021 has 4 divisors (see below), whose sum is σ = 21430332. Its totient is φ = 21411712.

The previous prime is 21420991. The next prime is 21421051. The reversal of 21421021 is 12012412.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (21420991) and next prime (21421051).

It can be written as a sum of positive squares in 2 ways, for example, as 11655396 + 9765625 = 3414^2 + 3125^2 .

It is a cyclic number.

It is not a de Polignac number, because 21421021 - 2¹⁷ = 21289949 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21420992 and 21421010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21421051) 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, 1581 + ... + 6733.

It is an arithmetic number, because the mean of its divisors is an integer number (5357583).

Almost surely, 2^21421021 is an apocalyptic number.

It is an amenable number.

21421021 is a deficient number, since it is larger than the sum of its proper divisors (9311).

21421021 is an equidigital number, since it uses as much as digits as its factorization.

21421021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9310.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21421021 is about 4628.2848875150. The cubic root of 21421021 is about 277.7239854889.

Adding to 21421021 its reverse (12012412), we get a palindrome (33433433).

The spelling of 21421021 in words is "twenty-one million, four hundred twenty-one thousand, twenty-one".