21511871 has 2 divisors, whose sum is σ = 21511872. Its totient is φ = 21511870.

The previous prime is 21511849. The next prime is 21511883. The reversal of 21511871 is 17811512.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21511871 - 2¹⁰ = 21510847 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21511871.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21511811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10755935 + 10755936.

It is an arithmetic number, because the mean of its divisors is an integer number (10755936).

Almost surely, 2^21511871 is an apocalyptic number.

21511871 is a deficient number, since it is larger than the sum of its proper divisors (1).

21511871 is an equidigital number, since it uses as much as digits as its factorization.

21511871 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 560, while the sum is 26.

The square root of 21511871 is about 4638.0891539512. The cubic root of 21511871 is about 278.1160557827.

The spelling of 21511871 in words is "twenty-one million, five hundred eleven thousand, eight hundred seventy-one".