21506249 has 4 divisors (see below), whose sum is σ = 21778560. Its totient is φ = 21233940.

The previous prime is 21506209. The next prime is 21506257. The reversal of 21506249 is 94260512.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21506249 - 2²⁴ = 4729033 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21506209) 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, 136037 + ... + 136194.

It is an arithmetic number, because the mean of its divisors is an integer number (5444640).

Almost surely, 2^21506249 is an apocalyptic number.

It is an amenable number.

21506249 is a deficient number, since it is larger than the sum of its proper divisors (272311).

21506249 is an equidigital number, since it uses as much as digits as its factorization.

21506249 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 272310.

The product of its (nonzero) digits is 4320, while the sum is 29.

The square root of 21506249 is about 4637.4830457911. The cubic root of 21506249 is about 278.0918256775.

The spelling of 21506249 in words is "twenty-one million, five hundred six thousand, two hundred forty-nine".