21149509 has 2 divisors, whose sum is σ = 21149510. Its totient is φ = 21149508.

The previous prime is 21149477. The next prime is 21149539. The reversal of 21149509 is 90594112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13432225 + 7717284 = 3665^2 + 2778^2 .

It is a cyclic number.

It is not a de Polignac number, because 21149509 - 2⁵ = 21149477 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21149539) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10574754 + 10574755.

It is an arithmetic number, because the mean of its divisors is an integer number (10574755).

Almost surely, 2^21149509 is an apocalyptic number.

It is an amenable number.

21149509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21149509 is an equidigital number, since it uses as much as digits as its factorization.

21149509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3240, while the sum is 31.

The square root of 21149509 is about 4598.8595325363. The cubic root of 21149509 is about 276.5456064606.

The spelling of 21149509 in words is "twenty-one million, one hundred forty-nine thousand, five hundred nine".