21505507 has 2 divisors, whose sum is σ = 21505508. Its totient is φ = 21505506.

The previous prime is 21505499. The next prime is 21505513. The reversal of 21505507 is 70550512.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21505507 - 2³ = 21505499 is a prime.

It is not a weakly prime, because it can be changed into another prime (21505007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10752753 + 10752754.

It is an arithmetic number, because the mean of its divisors is an integer number (10752754).

Almost surely, 2^21505507 is an apocalyptic number.

21505507 is a deficient number, since it is larger than the sum of its proper divisors (1).

21505507 is an equidigital number, since it uses as much as digits as its factorization.

21505507 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1750, while the sum is 25.

The square root of 21505507 is about 4637.4030448086. The cubic root of 21505507 is about 278.0886274364.

The spelling of 21505507 in words is "twenty-one million, five hundred five thousand, five hundred seven".