21257581 has 2 divisors, whose sum is σ = 21257582. Its totient is φ = 21257580.

The previous prime is 21257569. The next prime is 21257651. The reversal of 21257581 is 18575212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20385225 + 872356 = 4515^2 + 934^2 .

It is a cyclic number.

It is not a de Polignac number, because 21257581 - 2⁵ = 21257549 is a prime.

It is a super-2 number, since 2×21257581² = 903769499943122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21257521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10628790 + 10628791.

It is an arithmetic number, because the mean of its divisors is an integer number (10628791).

Almost surely, 2^21257581 is an apocalyptic number.

It is an amenable number.

21257581 is a deficient number, since it is larger than the sum of its proper divisors (1).

21257581 is an equidigital number, since it uses as much as digits as its factorization.

21257581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5600, while the sum is 31.

The square root of 21257581 is about 4610.5944302226. The cubic root of 21257581 is about 277.0158470778.

The spelling of 21257581 in words is "twenty-one million, two hundred fifty-seven thousand, five hundred eighty-one".