21432409 has 2 divisors, whose sum is σ = 21432410. Its totient is φ = 21432408.

The previous prime is 21432407. The next prime is 21432413. The reversal of 21432409 is 90423412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14462809 + 6969600 = 3803^2 + 2640^2 .

It is a cyclic number.

It is not a de Polignac number, because 21432409 - 2¹ = 21432407 is a prime.

Together with 21432407, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21432401) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10716204 + 10716205.

It is an arithmetic number, because the mean of its divisors is an integer number (10716205).

Almost surely, 2^21432409 is an apocalyptic number.

It is an amenable number.

21432409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21432409 is an equidigital number, since it uses as much as digits as its factorization.

21432409 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 21432409 is about 4629.5149853953. The cubic root of 21432409 is about 277.7731919895.

It can be divided in two parts, 214 and 32409, that added together give a palindrome (32623).

The spelling of 21432409 in words is "twenty-one million, four hundred thirty-two thousand, four hundred nine".