21430909 has 2 divisors, whose sum is σ = 21430910. Its totient is φ = 21430908.

The previous prime is 21430861. The next prime is 21430949. The reversal of 21430909 is 90903412.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16687225 + 4743684 = 4085^2 + 2178^2 .

It is a cyclic number.

It is not a de Polignac number, because 21430909 - 2⁷ = 21430781 is a prime.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21430949) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10715454 + 10715455.

It is an arithmetic number, because the mean of its divisors is an integer number (10715455).

Almost surely, 2^21430909 is an apocalyptic number.

It is an amenable number.

21430909 is a deficient number, since it is larger than the sum of its proper divisors (1).

21430909 is an equidigital number, since it uses as much as digits as its factorization.

21430909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 21430909 is about 4629.3529785489. The cubic root of 21430909 is about 277.7667116243.

The spelling of 21430909 in words is "twenty-one million, four hundred thirty thousand, nine hundred nine".