21815987 has 2 divisors, whose sum is σ = 21815988. Its totient is φ = 21815986.

The previous prime is 21815939. The next prime is 21815999. The reversal of 21815987 is 78951812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21815987 - 2¹² = 21811891 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21815887) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10907993 + 10907994.

It is an arithmetic number, because the mean of its divisors is an integer number (10907994).

Almost surely, 2^21815987 is an apocalyptic number.

21815987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21815987 is an equidigital number, since it uses as much as digits as its factorization.

21815987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 40320, while the sum is 41.

The square root of 21815987 is about 4670.7587178102. The cubic root of 21815987 is about 279.4205149666.

The spelling of 21815987 in words is "twenty-one million, eight hundred fifteen thousand, nine hundred eighty-seven".