21587521 has 2 divisors, whose sum is σ = 21587522. Its totient is φ = 21587520.

The previous prime is 21587509. The next prime is 21587549. The reversal of 21587521 is 12578512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19228225 + 2359296 = 4385^2 + 1536^2 .

It is a cyclic number.

It is not a de Polignac number, because 21587521 - 2¹⁹ = 21063233 is a prime.

It is not a weakly prime, because it can be changed into another prime (21587551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10793760 + 10793761.

It is an arithmetic number, because the mean of its divisors is an integer number (10793761).

Almost surely, 2^21587521 is an apocalyptic number.

It is an amenable number.

21587521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21587521 is an equidigital number, since it uses as much as digits as its factorization.

21587521 is an evil number, because the sum of its binary digits is even.

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

The square root of 21587521 is about 4646.2372948441. The cubic root of 21587521 is about 278.4416878453.

Subtracting from 21587521 its reverse (12578512), we obtain a palindrome (9009009).

The spelling of 21587521 in words is "twenty-one million, five hundred eighty-seven thousand, five hundred twenty-one".