21311987 has 2 divisors, whose sum is σ = 21311988. Its totient is φ = 21311986.

The previous prime is 21311981. The next prime is 21312001. The reversal of 21311987 is 78911312.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21311987 - 2²⁴ = 4534771 is a prime.

It is not a weakly prime, because it can be changed into another prime (21311981) 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, 10655993 + 10655994.

It is an arithmetic number, because the mean of its divisors is an integer number (10655994).

Almost surely, 2^21311987 is an apocalyptic number.

21311987 is a deficient number, since it is larger than the sum of its proper divisors (1).

21311987 is an equidigital number, since it uses as much as digits as its factorization.

21311987 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3024, while the sum is 32.

The square root of 21311987 is about 4616.4907668055. The cubic root of 21311987 is about 277.2519743639.

The spelling of 21311987 in words is "twenty-one million, three hundred eleven thousand, nine hundred eighty-seven".