21111521 has 2 divisors, whose sum is σ = 21111522. Its totient is φ = 21111520.

The previous prime is 21111509. The next prime is 21111523. The reversal of 21111521 is 12511112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20151121 + 960400 = 4489^2 + 980^2 .

It is a cyclic number.

It is not a de Polignac number, because 21111521 - 2⁶ = 21111457 is a prime.

Together with 21111523, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21111496 and 21111505.

It is not a weakly prime, because it can be changed into another prime (21111523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10555760 + 10555761.

It is an arithmetic number, because the mean of its divisors is an integer number (10555761).

Almost surely, 2^21111521 is an apocalyptic number.

It is an amenable number.

21111521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21111521 is an equidigital number, since it uses as much as digits as its factorization.

21111521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20, while the sum is 14.

The square root of 21111521 is about 4594.7275218450. The cubic root of 21111521 is about 276.3799334167.

Adding to 21111521 its reverse (12511112), we get a palindrome (33622633).

The spelling of 21111521 in words is "twenty-one million, one hundred eleven thousand, five hundred twenty-one".