21423421 has 2 divisors, whose sum is σ = 21423422. Its totient is φ = 21423420.

The previous prime is 21423403. The next prime is 21423487. The reversal of 21423421 is 12432412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14976900 + 6446521 = 3870^2 + 2539^2 .

It is a cyclic number.

It is not a de Polignac number, because 21423421 - 2⁷ = 21423293 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21423221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10711710 + 10711711.

It is an arithmetic number, because the mean of its divisors is an integer number (10711711).

Almost surely, 2^21423421 is an apocalyptic number.

It is an amenable number.

21423421 is a deficient number, since it is larger than the sum of its proper divisors (1).

21423421 is an equidigital number, since it uses as much as digits as its factorization.

21423421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 384, while the sum is 19.

The square root of 21423421 is about 4628.5441555634. The cubic root of 21423421 is about 277.7343571183.

Adding to 21423421 its reverse (12432412), we get a palindrome (33855833).

The spelling of 21423421 in words is "twenty-one million, four hundred twenty-three thousand, four hundred twenty-one".