21505513 has 2 divisors, whose sum is σ = 21505514. Its totient is φ = 21505512.

The previous prime is 21505507. The next prime is 21505531. The reversal of 21505513 is 31550512.

Together with next prime (21505531) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20313049 + 1192464 = 4507^2 + 1092^2 .

It is a cyclic number.

It is not a de Polignac number, because 21505513 - 2⁵ = 21505481 is a prime.

It is not a weakly prime, because it can be changed into another prime (21505543) 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, 10752756 + 10752757.

It is an arithmetic number, because the mean of its divisors is an integer number (10752757).

Almost surely, 2^21505513 is an apocalyptic number.

It is an amenable number.

21505513 is a deficient number, since it is larger than the sum of its proper divisors (1).

21505513 is an equidigital number, since it uses as much as digits as its factorization.

21505513 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 750, while the sum is 22.

The square root of 21505513 is about 4637.4036917223. The cubic root of 21505513 is about 278.0886532985.

The spelling of 21505513 in words is "twenty-one million, five hundred five thousand, five hundred thirteen".