21621871 has 2 divisors, whose sum is σ = 21621872. Its totient is φ = 21621870.

The previous prime is 21621851. The next prime is 21621881. The reversal of 21621871 is 17812612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21621871 - 2²¹ = 19524719 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21621851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10810935 + 10810936.

It is an arithmetic number, because the mean of its divisors is an integer number (10810936).

Almost surely, 2^21621871 is an apocalyptic number.

21621871 is a deficient number, since it is larger than the sum of its proper divisors (1).

21621871 is an equidigital number, since it uses as much as digits as its factorization.

21621871 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1344, while the sum is 28.

The square root of 21621871 is about 4649.9323650995. The cubic root of 21621871 is about 278.5892947810.

The spelling of 21621871 in words is "twenty-one million, six hundred twenty-one thousand, eight hundred seventy-one".