21257643 has 24 divisors (see below), whose sum is σ = 31436944. Its totient is φ = 12767040.

The previous prime is 21257581. The next prime is 21257651. The reversal of 21257643 is 34675212.

It is a de Polignac number, because none of the positive numbers 2^k-21257643 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21257643.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21257843) 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 in 23 ways as a sum of consecutive naturals, for example, 56805 + ... + 57177.

Almost surely, 2^21257643 is an apocalyptic number.

21257643 is a deficient number, since it is larger than the sum of its proper divisors (10179301).

21257643 is a wasteful number, since it uses less digits than its factorization.

21257643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 555 (or 544 counting only the distinct ones).

The product of its digits is 10080, while the sum is 30.

The square root of 21257643 is about 4610.6011538627. The cubic root of 21257643 is about 277.0161163930.

Subtracting 21257643 from its reverse (34675212), we obtain a square (13417569 = 3663²).

The spelling of 21257643 in words is "twenty-one million, two hundred fifty-seven thousand, six hundred forty-three".