21257491 has 2 divisors, whose sum is σ = 21257492. Its totient is φ = 21257490.

The previous prime is 21257479. The next prime is 21257519. The reversal of 21257491 is 19475212.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21257491 - 2¹³ = 21249299 is a prime.

It is not a weakly prime, because it can be changed into another prime (21257461) 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, 10628745 + 10628746.

It is an arithmetic number, because the mean of its divisors is an integer number (10628746).

Almost surely, 2^21257491 is an apocalyptic number.

21257491 is a deficient number, since it is larger than the sum of its proper divisors (1).

21257491 is an equidigital number, since it uses as much as digits as its factorization.

21257491 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5040, while the sum is 31.

The square root of 21257491 is about 4610.5846700825. The cubic root of 21257491 is about 277.0154561356.

The spelling of 21257491 in words is "twenty-one million, two hundred fifty-seven thousand, four hundred ninety-one".