21237409 has 2 divisors, whose sum is σ = 21237410. Its totient is φ = 21237408.

The previous prime is 21237407. The next prime is 21237413. The reversal of 21237409 is 90473212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20277009 + 960400 = 4503^2 + 980^2 .

It is a cyclic number.

It is not a de Polignac number, because 21237409 - 2¹ = 21237407 is a prime.

Together with 21237407, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21237407) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10618704 + 10618705.

It is an arithmetic number, because the mean of its divisors is an integer number (10618705).

Almost surely, 2^21237409 is an apocalyptic number.

It is an amenable number.

21237409 is a deficient number, since it is larger than the sum of its proper divisors (1).

21237409 is an equidigital number, since it uses as much as digits as its factorization.

21237409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3024, while the sum is 28.

The square root of 21237409 is about 4608.4063405911. The cubic root of 21237409 is about 276.9281962749.

The spelling of 21237409 in words is "twenty-one million, two hundred thirty-seven thousand, four hundred nine".