21123511 has 2 divisors, whose sum is σ = 21123512. Its totient is φ = 21123510.

The previous prime is 21123491. The next prime is 21123517. The reversal of 21123511 is 11532112.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21123511 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21123517) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10561755 + 10561756.

It is an arithmetic number, because the mean of its divisors is an integer number (10561756).

Almost surely, 2^21123511 is an apocalyptic number.

21123511 is a deficient number, since it is larger than the sum of its proper divisors (1).

21123511 is an equidigital number, since it uses as much as digits as its factorization.

21123511 is an evil number, because the sum of its binary digits is even.

The product of its digits is 60, while the sum is 16.

The square root of 21123511 is about 4596.0320930124. The cubic root of 21123511 is about 276.4322455840.

Adding to 21123511 its reverse (11532112), we get a palindrome (32655623).

The spelling of 21123511 in words is "twenty-one million, one hundred twenty-three thousand, five hundred eleven".