21045421 has 2 divisors, whose sum is σ = 21045422. Its totient is φ = 21045420.

The previous prime is 21045377. The next prime is 21045433. The reversal of 21045421 is 12454012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19900521 + 1144900 = 4461^2 + 1070^2 .

It is a cyclic number.

It is not a de Polignac number, because 21045421 - 2¹⁵ = 21012653 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21045461) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10522710 + 10522711.

It is an arithmetic number, because the mean of its divisors is an integer number (10522711).

Almost surely, 2^21045421 is an apocalyptic number.

It is an amenable number.

21045421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21045421 is an equidigital number, since it uses as much as digits as its factorization.

21045421 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 320, while the sum is 19.

The square root of 21045421 is about 4587.5288554951. The cubic root of 21045421 is about 276.0911840773.

Adding to 21045421 its reverse (12454012), we get a palindrome (33499433).

It can be divided in two parts, 21045 and 421, that multiplied together give a triangular number (8859945 = T₄₂₀₉).

The spelling of 21045421 in words is "twenty-one million, forty-five thousand, four hundred twenty-one".