21615871 has 2 divisors, whose sum is σ = 21615872. Its totient is φ = 21615870.

The previous prime is 21615851. The next prime is 21615907. The reversal of 21615871 is 17851612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21615871 - 2⁹ = 21615359 is a prime.

It is equal to p_1366447 and since 21615871 and 1366447 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21615851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10807935 + 10807936.

It is an arithmetic number, because the mean of its divisors is an integer number (10807936).

Almost surely, 2^21615871 is an apocalyptic number.

21615871 is a deficient number, since it is larger than the sum of its proper divisors (1).

21615871 is an equidigital number, since it uses as much as digits as its factorization.

21615871 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3360, while the sum is 31.

The square root of 21615871 is about 4649.2871496607. The cubic root of 21615871 is about 278.5635231844.

The spelling of 21615871 in words is "twenty-one million, six hundred fifteen thousand, eight hundred seventy-one".