21434509 has 4 divisors (see below), whose sum is σ = 22173660. Its totient is φ = 20695360.

The previous prime is 21434471. The next prime is 21434531. The reversal of 21434509 is 90543412.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 9030025 + 12404484 = 3005^2 + 3522^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21434509 is a prime.

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

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21434579) 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, 369532 + ... + 369589.

It is an arithmetic number, because the mean of its divisors is an integer number (5543415).

Almost surely, 2^21434509 is an apocalyptic number.

21434509 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

21434509 is a deficient number, since it is larger than the sum of its proper divisors (739151).

21434509 is an equidigital number, since it uses as much as digits as its factorization.

21434509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 739150.

The product of its (nonzero) digits is 4320, while the sum is 28.

The square root of 21434509 is about 4629.7417854563. The cubic root of 21434509 is about 277.7822639927.

The spelling of 21434509 in words is "twenty-one million, four hundred thirty-four thousand, five hundred nine".