21006287 has 2 divisors, whose sum is σ = 21006288. Its totient is φ = 21006286.

The previous prime is 21006281. The next prime is 21006289. The reversal of 21006287 is 78260012.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21006287 is a prime.

Together with 21006289, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21006281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10503143 + 10503144.

It is an arithmetic number, because the mean of its divisors is an integer number (10503144).

Almost surely, 2^21006287 is an apocalyptic number.

21006287 is a deficient number, since it is larger than the sum of its proper divisors (1).

21006287 is an equidigital number, since it uses as much as digits as its factorization.

21006287 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 21006287 is about 4583.2616115600. The cubic root of 21006287 is about 275.9199472026.

Adding to 21006287 its reverse (78260012), we get a palindrome (99266299).

The spelling of 21006287 in words is "twenty-one million, six thousand, two hundred eighty-seven".